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The detection of trace microRNAs (miRNA) is crucial for early cancer diagnosis. Here, a sensitive biosensor for miRNA directive detection was put forward, which was based on RNA‐templated palladium nanoparticles (PdNPs) signal amplification strategy. Uncharged peptide nucleic acids (PNA) probe was used to capture the target miRNA(T‐RNA) specifically. Subsequently, a large amount of palladium ions absorbed on T‐RNA strands via electrostatic forces, and the palladium nanocluster is rapidly generated based on chemical reduction. Obviously, RNA metallization method enables biosensor to be carried out efficiently at room temperature also simplifies the preparation and detection of the sensor. Under optimal conditions, this method can analyze the concentration of miRNA in the range of 10 fM to 1 nM, and the detection limit is 3.33 fM. At the same time, this method has strong anti‐interference ability in serum samples, which provides a broad prospect for the early screening and diagnosis of cancer. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensor was developed for the signal-on detection of sequence-specific DNA by exploiting potential-assisted Cu(I)-catalyzed azide-alkyne cycloaddition (φCuAAC) as an efficient approach for the labeling of hairpin-like oligonucleotide (hairpin) with electroactive probe. The hairpins, dually labeled with thiol and azide at either terminal, were firstly self-assembled on gold electrode and served as the capture probes for the specific recognition of target DNA. Upon hybridization with target DNA, the surface-confined hairpins were unfolded, liberating the azide-containing terminals away from electrode surface. Subsequently, the unfolded hairpins were conveniently and efficiently labeled with ethynylferrocene (EFC) via the φCuAAC. The quantitatively labeled EFC was finally measured via differential pulse voltammetry (DPV) for the signal-on electrochemical detection of sequence-specific DNA. The biosensor presented a good linear response over the range from 1 pM to 1 nM with a detection limit of 0.62 pM. Results also revealed that it was highly specific and held a good detection capability in serum samples. Furthermore, the ability to chemoselectively label hairpin-like oligonucleotide with signal reporter by electrical addressing, together with the simplicity and efficiency of the φCuAAC, makes it compatible with microfluidic devices and microelectrode arrays to achieve the miniaturized and multiplexed detections. [ABSTRACT FROM AUTHOR]

An efficient catalyst based on artificial bionic peroxidase was synthesized for electrocatalysis. A poly(ethyleneimine)/Au nanoparticle composite (PEI-AuNP) was prepared and it was then linked to hemin via a coupling reaction between carboxyl groups in hemin and amino groups in PEI without the activation of a carboxyl group by carbodiimide. Fourier transform infrared (FTIR) spectroscopy verified the formation of amido bonds within the structure. The presence of AuNPs contributed greatly in establishing the amido bonds within the composite. Transmission electron microscopy (TEM) and UV-visible spectroscopy were also used to characterize the PEI-AuNP–hemin catalyst. PEI-AuNP–hemin exhibited intrinsic peroxidase-like catalytic activities. The PEI-AuNP–hemin deposited on a glass carbon electrode had strong sensing for H2O2 with a well-defined linear relationship between the amperometric response and H2O2 concentration in the range from 1 μM to 0.25 mM. The detection limit was 0.247 nM with a high sensitivity of 0.347 mA mM−1 cm−2. The peroxidase-like catalytic activity of PEI-AuNP–hemin is discussed in relation to its microstructure. The study suggests that PEI-AuNP–hemin may have promising application prospects in biocatalysis and bioelectronics. [ABSTRACT FROM AUTHOR]

Since the oversecretion of protein kinases is indicative of multiple human diseases, the screening of their activities is quite important to clinical diagnosis and targeted therapy. In this work, an ultrasensitive peptide-based electrochemical biosensor was presented for the detection of protein kinase activity by using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique as a signal amplification strategy. First, the substrate peptides were tethered to a gold electrode surface via the thiol terminals. After the phosphorylation of substrate peptides by protein kinases, the carboxyl group-containing dithiobenzoates were labeled to the phosphorylated sites via the robust phosphate-Zr4+-carboxylate linkages. Finally, the RAFT polymerization was initiated using ferrocenylmethyl methacrylates (FcMMAs) and dithiobenzoates as the monomers and the RAFT agents, respectively. The grafting of ferrocenyl polymer chains efficiently recruits a great number of electro-active Fc probes to each phosphorylated site, leading to a drastic amplification of the electrochemical signal. With PKA (protein kinase A) as the target, the detection limit of the peptide-based biosensor can be as low as 1.05 mU mL−1. Moreover, it can selectively differentiate the target from other interferents and is applicable for the screening of potential inhibitors as well as the detection of protein kinase activity in complex cell lysates. Therefore, the peptide-based biosensor shows great promise as a universal tool for protein kinase activity detection and inhibitor screening. Image 1 • A peptide-based electrochemical biosensor is shown for protein kinase activity assay. • The RAFT polymerization is exploited as a novel signal amplification strategy. • The RAFT polymerization-based strategy is operationally simple and low-cost. • This assay is highly sensitive and selective and can be used for inhibitor screening. • It is applicable for protein kinase activity assay in complex biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • The use of nanozymes Mn-PCN-222 catalyzed ATRP makes the reaction oxygen tolerant and reduces the reaction requirements. • High binding affinity of host-guest pair, resulting in enhanced sensor stability. • This biosensor was successfully achieved in biological samples. In this work, a host-guest mediated electrochemical sensor for miRNA-21 via nanozymes Mn-PCN-222 catalysis was reported. In brief, the atom transfer radical polymerization (ATRP) reaction was enabled via the continuous conversion of hydrogen peroxide (H 2 O 2) to hydroxyl radicals (HO∙) via Mn-PCN-222. Specifically, miRNA-21 was captured and immobilized on the surface of an indium tin oxide (ITO) electrode using complementary DNA (Cp-DNA). In this way, miRNA-21 provided a sequence that can hybridize with F-DNA(ferrocene modified DNA primer). At the same time, an ATRP initiator (β-CD-Br 15) was attached to the electrode through host-guest interaction. The controlled polymerization of ferrocene methyl methacrylate (FcMMA) using β-CD-Br 15 for continuous activator regeneration (ICAR) ATRP yields polymer FcMMA n with a high square wave voltammetry (SWV) signal in the presence of target miRNA-21. Without added miRNA-21, a lower SWV current was observed because β-CD-Br 15 was not successfully modified onto the ITO electrode. The biosensor has also been used in the detection of serum samples. Moreover, the proposed host-guest mediated electrochemical biosensor has potential in bioanalytical applications for sensitive detection of biomolecules. [ABSTRACT FROM AUTHOR]

In this work, a novel electrochemical biosensor based on nitronyl nitroxide monoradical 2,2,6,6-tetramethylpiperidine 1-Oxyl (TEMPO) as new electrochemical label for facile nucleic acids detection is developed. This fast and convenient functional microelectrode was designed by fixing the capture probe peptide nucleic acid (PNA) and using the coordination interaction of Zr4+ with both phosphate groups and carboxyl groups. Differential pulse voltammetry (DPV) was used to study the oxidation current of TEMPO which was combined with the electrode surface and labeled. TEMPO electrochemical signal related to target deoxyribonucleic acid (tDNA) concentration was finally detected when tDNA was added on the surface of glassy carbon electrode (GCE). The detection principle, optimization of key factors and performance analysis of the biosensor are also discussed. A great linear relation is acquired within the scope of 10 pM–100 nM under optimal conditions and the detection limit of this experiment is calculated as low as 2.57 pM (R2 = 0.996). In addition, complex serum samples were used to explore the practical application of this experiment. The results show the developed electrochemical DNA biosensor has wide application prospects in nucleic acids detection and clinical analysis. Image 1 • A novel electrochemical biosensor is developed for nucleic acids detection. • The biosensor is based on nitronyl nitroxide TEMPO as an electrochemical label. • Stable free radical TEMPO as electrochemical detection signal is proposed firstly. • The biosensor shows high sensitivity, specificity and simple manufacturability. [ABSTRACT FROM AUTHOR]

Uric acid (UA), scavenger of oxygen radical, is a very important antioxidant that help maintains the stability of blood pressure and antioxidant stress. However, an abnormal UA concentration may be connected with many diseases: a higher UA concentration, comings from improper lifestyle such as purine excessive intake and excessive drinking, may reveal hyperuricemia, gout and some cardiovascular diseases; meanwhile, some genetic diseases can result in a low level UA relatively for a long time. Therefore, to develop a rapid and accurate detection method of UA is urgent and important. Recently many detection methods have been developed to measure the level of UA in human serum and urine sample even saliva and nails and tears. This review outlines the importance of UA detection and the history of the development of UA detection methods. UA detection include spectral (ultraviolet absorption, fluorescence), electrochemical (voltammetry, electrochemiluminescence, surface plasmon resonance), chromatography (liquid and gas phase), capillary electrophoresis and isotope dilution mass spectrometry, etc. Most of the above detection methods contain both enzymatic and nonenzymatic strategies. The materials used in mentioned methods above tend to be diversified, hence an overview of materials used in UA detection are also reported. [ABSTRACT FROM AUTHOR]

[Display omitted] • A DNA sensor based on atom transfer radical polymerization (ATRP) was designed. • Photo-ATRP based on catalyst 10-phenylphenothiazine was first applied in biosensor. • The biosensor has highly sensitive to t-DNA with a detection limit of 79 aM. • The biosensor was successfully used for detection of DNA in biological samples. The development of ultrasensitive deoxyribonucleic acid (DNA) sensors related to the disease is of great significance for early diagnosis and prevention of the disease. Here, an ultrasensitive DNA sensor based on the photocatalytic atom transfer radical polymerization (photo-ATRP) strategy was prepared. In this strategy, the target DNA was specifically recognized by sulfhydryl-modified peptide nucleic acid (PNA), and α-bromophenylacetic acid (BPAA) was grafted onto the DNA via phosphate-Zr(IV)-carboxylate. In the presence of photocatalyst 10-phenylphenothiazine (PTH), α-Br was reduced under 365 nm UV light to generate active radicals, and the polymer chain containing electrochemical signaling molecule (ferrocene) was introduced to the electrode surface by mediated ATRP. Finally, the peak current value was measured by square wave voltammetry (SWV) and the concentration of DNA was evaluated. The biosensor was constructed based on a green strategy for ATRP reaction without using a heavy metal catalyst (metal-free), thus reducing the pollution of the environment. Moreover, under optimal conditions, the relationship between the DNA sensor and the target was linear in the concentration range of 0.1 fM ∼ 10 pM, and the limit of detection was 79 aM. The sensor has the advantages of high sensitivity, interference-free and good stability, which indicates that it has great practical application potential in the field of life science and medical research. [ABSTRACT FROM AUTHOR]

Flunitrazepam, a very potent benzodiazepine with sedative, hypnotic and amnesic effects, is commonly used to treat severe insomnia and as an anesthetic. Due to these characteristics, when flunitrazepam is sneaked into alcohol or drinks, it is often highly associated with violent behavior and drug rape cases. Therefore, it is also known as a "date rape drug", and the detection of flunitrazepam and its metabolites is of great interest in forensic medicine and pharmacotoxicology. This paper describes the mechanism of action and drug metabolism process of flunitrazepam, reviews the different methods for detecting flunitrazepam published over the years, summarizes the detection limits of each method and compares their advantages and disadvantages. We hope to provide some inspiration for future research in this field. [ABSTRACT FROM AUTHOR]

A green electrochemical biosensor was developed based on metal-organic framework (MOF)-catalyzed atom transfer radical polymerization (ATRP) for quantifying miRNA-21, used as the proof-of-concept analyte. Unlike conventional ATRP, Mn-PCN-222 (PCN, porous coordination network) could be used as an alternative for green catalyst to substitute traditional catalysts. First, poly (diallyldimethylammonium chloride) (PDDA) was fixed on the surface of the indium tin oxide (ITO) electrode, and then the Mn-PCN-222 was linked to ITO electrode via electrostatic binding with PDDA. Next, aminated ssDNA (NH2-DNA) was used to modify the electrode further by amide reaction with Mn-PCN-222. Then, the recognition and hybridization of NH2-DNA with miRNA-21 prompt the generation of DNA−RNA complexes, which further hybridize with Fc-DNA@β-CD-Br15 and permit the initiator to be immobilized on the electrode surface. Accordingly, β-CD-Br15 could initiate the polymerization of ferrocenylmethyl methacrylates (FcMMA) under the catalysis of MOF to complete the ATRP reaction. FcMMA presented a distinct electrochemical signal at ~ 0.33 V. Taking advantage of the unique multi-site properties of β-CD-Br15 and the efficient catalytic reaction induced by Mn-PCN-222, ultrasensitive detection of miRNA-21 was achieved with a detection limit of 0.4 fM. The proposed electrochemical biosensor has been applied to the detection of miRNA-21 in serum samples. Therefore, the proposed strategy exhibited potential in early clinical biomedicine. [ABSTRACT FROM AUTHOR]

Preeclampsia (PE) seriously affects pregnant women and fetuses' health and causes maternal near-misses. CD81 has been confirmed to be a novel PE biomarker with great potential. Herein, a hypersensitive dichromatic biosensor based on the plasmonic enzyme-linked immunosorbent assay (plasmonic ELISA) is proposed initially for the application of CD81 in early screening for PE. In this work, a novel chromogenic substrate [(HAuCl4)-(N-methylpyrrolidone)-(Na3C6H5O7)] is designed based on the H2O2 dual catalysis reduction pathway of Au ions. The two reduction pathways of Au ions are controlled by H2O2 which ensures that the synthesis and growth of AuNPs are sensitive to H2O2. The amount of H2O2 correlates with the concentration of CD81 and directs the production of different-sized AuNPs in this sensor. Blue solutions are generated when analytes are present. When analytes are absent, solutions turn red. Therefore, due to different absorption peaks in red and blue, bimodal detection can be performed, and then two detection signals can be generated, one on signal at 550 nm and another off signal at 600 nm. This method exhibits a linear response to the logarithmic CD81 concentrations in the range of 0.1–1000 pg mL−1 with detection limits of 86 fg mL−1 and 152 fg mL−1 at two wavelengths. The false positive rate is low due to the nonspecific coloration caused by serum, which produces a more intense color contrast. The results indicate that the proposed dichromatic sensor could be used as a visual sensing platform for the direct detection of CD81 in biological samples and demonstrate its potential in preeclampsia diagnosis. [ABSTRACT FROM AUTHOR]

The ability to directly detect double-stranded DNA (dsDNA) without sequence-preference continues to be a major challenge. Herein, we report an electrochemical method for the direct, highly sensitive detection of dsDNA based on the strand replacement of dsDNA by peptide nucleic acid (PNA) and the in situ growth of electroactive polymers through the surface-initiated electrochemically mediated atom transfer radical polymerization (SI-eATRP). Thiolated PNA molecules are firstly self-assembled onto gold electrode surface for the specific recognition of target dsDNA (dsDNA-T), which in turn leads to the formation of a high density of PNA/DNA heteroduplexes on the electrode surface for the subsequent attachment of ATRP initiators via the phosphate-Zr 4+ -carboxylate chemistry. By applying a negative potential to the electrode, the air-stable Cu II deactivators can be reduced into the Cu I activators so as to trigger the surface-initiated polymerization for the in situ growth of electroactive polymers. Due to the strand replacement of dsDNA by PNA, dsDNA can be directly detected without sequence-preference. Besides, the growth of polymers enables the modification of numerous electroactive probes, thereby greatly improving the electrochemical signal. Under optimal conditions, a good linearity between the electrochemical signal and the logarithm of dsDNA-T concentration over the range from 1.0 fM to 1.0 nM, with a detection limit of 0.47 fM, can be obtained. Results indicate that it is highly selective, and holds high anti-interference capability in the presence of human serum samples. Therefore, this method offers great promises in providing a universal and efficient solution for the direct detection of dsDNA. [ABSTRACT FROM AUTHOR]

In this paper, a photocatalytic system for effectively degrading azo dyes is described. The nanostructured porous Al 2 O 3 layer on glass substrate (PAOG)/silver nanoparticles (AgNPs)–Hemin composites were synthesized via photochemical reduction of Ag, self-assembly of 11-mercaptoundecanoic acid (MUA) on AgNPs and subsequently linking Hemin to MUA via coordination bond. PAOG as a nanoporous template was chemically durable, highly porous and allowed chemicals conveniently immobilized on the glass surface. PAOG had a BET surface area of 151 m 2 /g which facilitated the immobilization of AgNPs. The composite was characterized by BET surface area measurements, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The photoreaction degradation processes were examined by UV/vis spectroscopy. Methyl orange (MO) and Acid red 18 solutions were used to evaluate the photocatalytic performance of PAOG/AgNPs–Hemin composite under visible light and UV irradiation. Compared with PAOG/Hemin, the PAOG/AgNPs–Hemin composite had enhanced photocatalytic efficiency due to higher electron transfer efficiency from AgNPs to Hemin. This novel composite with enhanced broad spectrum photocatalytic properties has promising potentials in degradation of dyes by UV and visible light utilization. [ABSTRACT FROM AUTHOR]

Poly(thymine) (polyT) and double-stranded DNA (dsDNA) can act as efficient templates for the formation of copper nanoparticles (CuNPs) at a low concentration of CuSO4, and the formed CuNPs emit excellent fluorescence. In this work, we demonstrated a new and facile strategy for the highly sensitive and selective detection of DNA on streptavidin-functionalized magnetic beads (SA-MB) using DNA-templated CuNPs as the fluorescent probe. Target DNA (tDNA) was hybridized with the capture DNA that was immobilized on the surface of SA-MB. Surface initiated enzymatic polymerization (SIEP) was employed as the signal amplification method to generate the polyT at the 3′ end of tDNA for the formation of CuNPs. The incorporation of polyT by SIEP resulted in ∼35.7 fold signal amplification compared to the dsDNA after hybridization without SIEP. A dose–response curve for detection of DNA was obtained, with a linear dynamic range of 0.1 nM to 10 nM. We showed that this method has a low pM limit of detection (LOD 98.2 pM) and it is also very sensitive to the mismatch type in a specific DNA sequence. In addition, it avoids rigorously controlled temperature, complex synthesis of the fluorescent probe and prelabeling of DNA strands and eliminates the use of sophisticated experimental techniques and equipment. Armed with these intriguing properties, the proposed system could provide an efficient tool for early diagnosis and risk assessment of malignancy. [ABSTRACT FROM AUTHOR]

Thrombin, a coagulation system protease, is a key enzyme involved in the coagulation cascade and has been developed as a marker for coagulation disorders. However, the methods developed in recent years have the disadvantages of complex operation, long reaction time, low specificity and sensitivity. Meanwhile, thrombin is at a lower level in the pre-disease period. Therefore, to accurately diagnose the disease, it is necessary to develop a fast, simple, highly sensitive and specific method using signal amplification technology. We designed an electrochemical biosensor based on photocatalytic atom transfer radical polymerization (photo-ATRP) signal amplification for the detection of thrombin. Sulfhydryl substrate peptides (without carboxyl groups) are self-assembled to the gold electrode surface via Au–S bond and serve as thrombin recognition probes. The substrate peptide is cleaved in the presence of thrombin to generate –COOH, which can form a carboxylate-Zr(IV)-carboxylate complex via Zr(IV) and initiator (α-bromophenylacetic acid, BPAA). Subsequently, an electrochemical biosensor was prepared by introducing polymer chains with electrochemical signaling molecules (ferrocene, Fc) onto the electrode surface by photocatalytic (perylene, Py) mediated ATRP using ferrocenylmethyl methacrylate (FMMA) as a monomer. The concentration of thrombin was evaluated by the voltammetric signal generated by square wave voltammetry (SWV), and the result showed that the biosensor was linear between 1.0 ng/mL ∼ 10 fg/mL, with a lower detection limit of 4.0 fg/mL (∼0.1 fM). Moreover, it was shown to be highly selective for thrombin activity in complex serum samples and for thrombin inhibition screening. The biosensor is an environmentally friendly and economically efficient strategy while maintaining the advantages of high sensitivity, anti-interference, good stability and simplicity of operation, which has great potential for application in the analysis of complex samples. [Display omitted] • A thrombin sensor based on atom transfer radical polymerization was designed. • Photo-ATRP based on catalyst perylene was first applied in biosensor. • The biosensor has highly sensitive to thrombin with a detection limit of 4.0 fg/mL. • The biosensor has good anti-interference ability in 0–20% normal human serum. [ABSTRACT FROM AUTHOR]

A simple dansylated tryptophan (DW) fluorescent sensor has been synthesized for highly selective and sensitive detection of Hg2+ over other common metal ions by chelation enhanced fluorescence (CHEF) and solvatochromic effects, and the interaction between DW and Hg2+ were investigated by IR and NMR. [Display omitted] • A new dansylated tryptophan fluorescence sensor was synthesized and characterized. • The sensor displayed an excellent selectivity and high sensitivity for Hg2+. • The sensing mechanism for Hg2+ was via CHEF and solvatochromic effects. • The interaction between the sensor and Hg2+ were studied by IR and NMR. A new fluorescent sensor of dansylated tryptophan (DW) was synthesized using solid phase peptide synthesis (SPPS). Upon the addition of different metal ions, only the presence of Hg2+ induced an increase in DW fluorescence intensity with a blue shift from 550 to 496 nm. DW was highly sensitive and selective for detecting Hg2+ with a low detection limit of 6.53 nM in 20 mM HEPES buffer (pH 7.4). The turn-on response could be attributed to the combination of chelation enhanced fluorescence (CHEF) and solvatochromic effects. The binding constant of DW with Hg2+ ion was determined to be 9.4 × 104 M−1/2 with a stoichiometric ratio of 2: 1. The DW + Hg2+ complex can be reversed with EDTA and reused with excellent circulation effect. The fluorescence lifetime and absolute quantum yield of DW were studied before and after the addition of Hg2+. Further characterizations of the interaction between DW and Hg2+ were conducted by IR and NMR. [ABSTRACT FROM AUTHOR]

A universal and straightforward electrochemical biosensing strategy for the detection and identification of sequence-specific DNA via click chemistry-mediated labeling of hairpin DNA probes (hairpins) with ethynylferrocene was reported. In the target-unbound form, the immobilized hairpins were kept in the folded stem–loop configuration with their azido terminals held in close proximity of the electrode surface, making them difficult to be labeled with ethynylferrocene due to the remarkable steric hindrance of the densely packed hairpins. Upon hybridization, they were unfolded and underwent a large conformational change, thus enabling the azido terminals to become available for its subsequent conjugation with ethynylferrocene via the Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC). After that, the quantitatively labeled ethynylferrocene could be exploited as the electroactive probes to monitor the DNA hybridization. As the unfolded hairpins were labeled in a stoichiometric ratio of 1 : 1, the electrochemical measurement based on differential pulse voltammetry enabled a reliable quantification of sequence-specific DNA. Under optimal conditions, the strategy could detect target single-stranded DNA (ssDNA) down to 0.296 pM with a good linear response over the range from 1 pM to 1 nM, and had excellent specificity in the genotyping of single-nucleotide polymorphisms. Furthermore, it also exhibited good detection reliability in serum samples and required no complicated protocols. More importantly, the simplicity of this strategy together with its compatibility with microfluidic chips makes it show great potential in clinical applications, where simple procedures are generally preferred. [ABSTRACT FROM AUTHOR]

In this work, we presented a novel signal amplification approach to construct an electrochemical DNA biosensor for the ultrasensitive determination of sequence-specific DNA by exploiting hematin as biomimetic catalyst toward in situ metallization. Briefly, thiolated peptide nucleic acid (PNA) probes were firstly immobilized onto gold electrode through the formation of self-assembled monolayer (SAM) and then hybridization was accomplished in the ensuing step. After that, hematin molecules were introduced to the hybridized PNA/DNA heteroduplexes by employing phosphate–zirconium–carboxylate coordination chemistry. Next, the attached hematin molecules acted as catalyst in accelerating the reduction of silver ions in the presence of catechol, leading to the in situ deposition of silver particles onto the electrode. Finally, the deposited silver particles were electrochemically stripped into KCl solution and measured by square wave voltammetry (SWV). Under optimal conditions, the hematin-based electrochemical DNA biosensor presented a good linear relationship between the stripping peak currents and logarithm of single-stranded DNA (ssDNA) concentrations in the range from 0.1 fM to 0.1 nM with a low detection limit of 62.41 aM, and it rendered satisfactory analytical performance for the determination of ssDNA in serum samples. Furthermore, it exhibited good reproducibility and stability, meanwhile, it also showed excellent specificity toward single-nucleotide polymorphism (SNP). Therefore, the hematin-based signal amplification approach has great potential in clinical applications and is also suitable for quantification of biomarkers at ultralow level. [ABSTRACT FROM AUTHOR]

An electrochemical method is described for the ultrasensitive determination of sequence-specific DNA by using polysaccharide-mediated in-situ deposition of metallic silver on a gold electrode. Specifically, a thiolated peptide nucleic acid (PNA) is immobilized on the gold electrode via formation of a self-assembled monolayer. Following hybridization between PNA and target single-stranded DNA (ssDNA), polygalacturonic acid (PGUA) is introduced to the PNA/DNA heteroduplexes via phosphate-zirconium-carboxylate coordination interaction. Next, the vicinal hydroxy groups of the polysaccharide backbone are cleaved and oxidized into aldehyde groups. These act as reductants and convert added silver ions into metallic silver which in-situ deposits on the gold electrode, and then is stripped off electrochemically into a solution of KCl where it is accurately determined by differential pulse voltammetry. Under optimal conditions, this assay exhibits a wide linear response range in that the stripping current is related to the logarithm of the concentration of target ssDNA in the 0.1 fM to 10 pM range, with a detection limit as low as 2.5 aM. The method displays excellent specificity in clearly differentiating mismatched oligonucleotide fragments. We therefore believe that this method has a large potential in terms of genotyping of single-nucleotide polymorphism. Moreover, this kind of signal amplification possesses a very large capability with respect to ultrasensitive quantitation of low-abundant biomarkers. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel fluorescence assay is proposed through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) strategy for alkaline phosphatase (ALP) activity detection. First of all, 2-bromo-2-methylpropionic acid (BMP) was employed as the initiator to modify on the surface of the magnetic nanoparticle (Fe3O4-MNP) by amide bonding. Then, ascorbic acid (AA) produced by ALP catalyzed the phosphate group removal from L-ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS), which underwent a redox reaction with Cu(II) and the product Cu(I) triggered the ARGET ATRP reaction. Finally, a strong fluorescent signal could be detected at 514 nm due to numerous fluorescent monomers being grafted to the Fe3O4-MNPs surface (Ex = 490 nm, Em = 514 nm). Under optimal experimental conditions, the linear range of this fluorometric assay for ALP activity was 1–80 mU mL−1, and the detection limit was 0.68 mU mL−1. The method exhibited excellent selectivity and satisfactory results were obtained in the inhibition rate and human serum experiments. Therefore, this ALP activity detection strategy has great potential for clinically relevant disease detection and drug screening. A novel fluorescence strategy for alkaline phosphatase activity detection based on the dephosphorylation property of alkaline phosphatase and ARGET ATRP reaction. [ABSTRACT FROM AUTHOR]

Assembling functional molecules on the surface of an enzyme electrode is the most basic technique for constructing a biosensor. However, precise control of electron transfer interface or electron mediator on the electrode surface remains a challenge, which is a key step that affects the stability and sensitivity of enzyme-based biosensors. In this study, we propose the use of controllable free radical polymerization to grow stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) polymer as electron mediator on enzyme surface for the first time. Through scanning electron microscopy (SEM), Raman spectroscopy, electrode surface coverage measurement, static contact angle (SCA), and a series of electrochemical methods, it has been demonstrated that the TEMPO-based enzyme electrode exhibits a uniform hydrophilic morphology and stable electrochemical performance. Furthermore, the results show that the sensor demonstrates high sensitivity for detecting glucose biomolecules in artificial sweat and serum. Attributing to the quantitative and controllable radical polymerization of TEMPO redox assembled enzyme electrode surface, the as-proposed biosensor providing a use, storage, and inter-batch sensing stability, providing a vital platform for wearable/implantable biochemical sensors. • Controllable free radical polymerization of TEMPO polymer on enzyme surface. • Stable and conductive TEMPO work as electron mediator for an enzyme electrode. • Highly stable assembly interface providing a use, storage, and inter-batch stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developing a novel biosensor to detect miRNA-21 based on PET-RAFT signal amplification. • PET-RAFT catalyzed by erythrosin B was first applied to biosensor. • The biosensor has highly sensitive to miRNA-21 with a detection limit of 12.4 aM. • The biosensor exhibits an excellent anti-interference ability in serum samples. Quantitative detection of the cancer-associated biomarker miRNA-21 is essential for the prevention and treatment of early-stage cancer patients. In the early diagnosis of cancer, due to the low concentration of miRNA in the organism, it is necessary to develop a fast, simple, highly sensitive and specific method using signal amplification techniques. Herein, a photo-induced electron/energy transfer reversible addition-fragmentation chain transfer polymerization signal amplification electrochemical biosensor was developed. Peptide nucleic acid was used as the recognition probe for miRNA-21 and the chain transfer agent (4-cyano-4-(dodecylsulfonylsulfanylthiocarbonyl)sulfonylpentanoic acid) bearing a carboxylic acid group was successfully conjugated with a phosphate group in the presence of ZrOCl 2 to form the phosphate-Zr(IV)-carboxylic acid complex. Subsequently, the polymerization of the monomer (ferrocenylmethyl methacrylate) was achieved by blue light irradiation in the presence of erythrosin B (higher triple quantum yield) and triethanolamine (increases electron transfer rate). With this sophisticated signal amplification biosensing platform, low detection limit of 12.4 aM was achieved for miRNA-21. The biosensor reduces costs and simplifies experimentation while ensuring high sensitivity and selectivity. Meanwhile, the biosensor exhibits excellent anti-interference ability in serum samples and has great potential for practical applications in the early prevention of cancer. [ABSTRACT FROM AUTHOR]

An original electrochemical biosensor via Cu-mediated near-infrared light (NIR) polymerization was reported for highly sensitive nucleic acid detection. Lung cancer DNA as nucleic acid model was specifically recognized via phosphate-free peptide nucleic acid (PNA). Subsequently, initiators of polymerization were attached to PNA/DNA heteroduplex under the assistance of phosphate-Zr4+-carboxylate. Cu 2 (OH)PO 4 and H 2 O 2 system was triggered off under the irradiation of NIR light, and then hydroxyl radicals (•OH) were produced. At the same time, carbon-based radicals were also generated through the reaction between •OH and methacrylic monomers of polymerization, which initiated the photoinduced polymerization. Then, numerous ferrocene-based methacrylic monomers were modified on the surface of electrode. The limit of detection was improved to 2.6 fM with linear range from 0.01 pM to 1000 pM (R2 = 0.993), and the minimum molar number of lung cancer DNA was 26 zmol (in 10 μL). This biosensor also presented portable and cost-efficient feature due to simple operation and ubiquitous light, and no phototoxicity and good tissue penetration of NIR also endowed this strategy great potential in biological detection. • NIR was first designed for highly sensitive nucleic acid detection. • Cu 2 (OH)PO 4 was firstly used to activate photoinduced polymerization. • The operation of this biosensor was simple. • This biosensor presented a portable and cost-efficient feature. [ABSTRACT FROM AUTHOR]

[Display omitted] • FADH 2 was used as a catalyst for ATRP system to detect microRNA-21 for the first time. • FADH 2 as ATRP catalyst can reduce the damage of organic reagents to the sandwich structure of nucleic acids. • The mechanism of FADH 2 polymerization in ATRP was studied. • A highly specific and sensitive microRNA-21 biosensor based on FADH 2 was developed. • The applicability of the method was confirmed by the detection of microRNA-21 added to human serum. For early diagnosis of disease, ultrasensitive mircoRNA-21 detection has considerable potential. In this paper, an ultra-sensitive fluorescence detection method for microRNA was developed by atom transfer radical polymerization (ATRP). This ATRP reaction was first initiated by using flavin mononucleotide (FADH 2). The DNA probe 1 modified with amino group was fixed on the magnetic nanoparticle Fe 3 O 4 , and microRNA-21 was added to form the probe 1-microRNA-21. Another carboxy-modified DNA 2 forms a sandwich structure with the bound microRNA-21. Two terminally modified DNA types are used as microRNA probes, using complementary base pairing to form a stable super-sandwich structure between the DNA probe and the microRNA. Under optimal conditions, microRNA was detected in PBS buffer with a detection limit of 0.19 fM. And even in 10% of human serum, microRNA-21 can be detected with a detection limit of 47.8 fM. Results show that this method has high selectivity, efficiency and stability, which broad application prospect in microRNA ultra-sensitive detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vitamin B 12 is milder and more efficient as an electrically initiated catalyst; • Monomer polymerization downed the detection limit to 1.010 fM. • Polymer chains are extremely stable and can be stored for long periods of time. Vitamin B 12 being a natural catalyst in atom transfer radical polymerization (ATRP), has the advantages of mild reaction conditions, good biocompatibility and high catalytic efficiency. In this report, an electrochemical biosensor of the lung cancer biomarker microRNA-21 (miRNA-21) is designed for early screening of lung cancer with high sensitivity at the femtomolar level. In this approach, hairpin DNA with N 3 end group was first attached to the electrode surface. When miRNA-21 was present and paired with hairpin DNA, the N 3 group released and attached to the ATRP initiator through "click reaction". Through eATRP, a large number of FerrocenylMethyl Methacrylate (FcMMA) monomers polymerized into long chains for signal amplification. These long chains had a distinct electrical signal in the square wave voltammetry (SWV), which can detect RNA with high sensitivity. The limit of detection (LOD) goes down to 1.010 fM after ATRP polymerization, which is lower than that of the majority of other ultra-sensitive RNA electrochemical assays. Results also show that the vitamin B 12 -based electrochemical biosensor is highly selective and suitable for RNA detection in complex biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly selective and ultrasensitive DNA detection method was developed by utilizing target cycle and ATRP. • The optimized biosensor was capable of detecting 1.954 aM target DNA (12 molecules DNA can be detected in a 10 μL system). • This signal amplification strategy can be applied for the detection of protein and other biological molecular. We propose a novel electrochemical biosensor platform with triple helix structure as switch, Exonuclease III (Exo III)-mediated target cycle at 2-D level and electrochemical-mediated atom transfer radical polymerization (ATRP) at 3-D level as double signal amplification strategy for nucleic acid detection with ultra-sensitivity and high-selectivity. In this strategy, triple-helical DNA modified with N 3 was first constructed on the gold electrode (AuE) surface. Exo III mediated target cycle was then triggered in the presence of Target DNA. N 3 was released and exposed on the AuE surface, owing to the triple helix structure was destroyed in this process. propargyl-2-bromoisobutyrate (PBIB), the initiator of ATRP, was then introduced to the biosensor surface via click chemistry. Finally, electrochemically mediated ATRP polymerizes a large amount of electroactive monomer, ferrocene methacrylate (FMMA), onto the AuE surface. The target circulates to make target DNA reused at the 2-D level, and ATRP polymerizes a large number of electrochemical signal molecules at the 3-D level, making the biosensor detection limit as low as 1.954 aM. Moreover, the linear range of target DNA detection reaches 7 orders of magnitude (10 aM-10 fM, R2 = 0.993). In addition, the biosensor shows excellent anti-interference ability when analyzing DNA in serum samples. In short, the preparation method is rapid, simple, easy to operate, and has potential applications in biological analysis. [ABSTRACT FROM AUTHOR]

The concentration level of cytokeratin fragment antigen 21-1 (CYFRA21-1) can be used as an important indicator for predicting non–small cell lung cancer (NSCLC). Here, a sandwich-type electrochemical immunosensor for ultrasensitive detection of CYFRA21-1 is developed. The sensor based on a combination of gold nanoparticle (AuNPs) decorated Ti3C2Tx-MXene (Au-Ti3C2Tx) as the substrate enhancer, and toluidine blue (TB) modified AuNPs doped covalent organic framework (COF) polymer as the signal tag (TB-Au-COF). The Au-Ti3C2Tx is used to capture numerous primary antibodies and accelerate the electron transfer rate of the substrate, while the TB-Au-COF can be applied to provide a large number of signal units TB and secondary antibodies. These features of composites endow the proposed immunosensor with high sensitivity and current response to CYFRA21-1. Under optimum conditions, the immunosensor offers a wide current response for CYFRA21-1 from 0.5–1.0 × 104 pg·mL−1 with a detection limit of 0.1 pg·mL−1. Furthermore, the biosensing platform can be applied for CYFRA21-1 detection to analyze real serum samples, providing an effective and useful avenue for the applicability of Au-Ti3C2Tx and TB-Au-COF composite materials in biosensing field. [ABSTRACT FROM AUTHOR]

Improving the sensitivity of detection is crucial to monitor biomarker, assess toxicity, and track therapeutic agent. Herein, a sensitivity-improved immunosensor is reported for the first time via functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy. Through the ROP reaction using 2-[(4-ferrocenylbutoxy)methyl] oxirane (FcEpo) as the monomer, lots of electroactive tags are linked in situ from multiple initiation sites on the GO surface modified with ethanol amine (GO-ETA), thereby achieving high sensitivity even in the case of trace amounts of tumor markers. The utmost important factor for achieving this high sensitivity is to select functionalized GO as the initiator that contains a large number of repeated hydroxyl functional groups so as to trigger additional ROP reaction. Under the optimal conditions, the high sensitivity and applicability is demonstrated by the use of GO-ETA-mediated ROP-based immunosensor to detect non-small cell lung cancer (NSCLC)–specific biomarker down to 72.58 ag/mL (equivalent to ~6 molecules in a 5 μL sample). Furthermore, the satisfactory results for the determination of biomarkers in clinical serum samples highlighted that this immunosensor holds a huge potential in practical clinical application. [ABSTRACT FROM AUTHOR]

In this paper, a high sensitivity and accuracy biosensor for CEA detection based on atom transfer radical polymerization (ATRP) with β-cyclodextrin (β-CD) and 2-bromoisobutyryl bromide (BIBB) as a macroinitiator is reported for the first time. Carcinoembryonic antigen (CEA), as a tumor-associated antigen, can be of great significance in the diagnosis of illness. Herein, thiolated CEA-aptamer 1 (Apt 1) at the 5′-terminal is first immobilized on amino magnetic beads (MBs) via a cross-linking agent to specifically recognize the antigen of CEA. After the sandwich-type structure formed, β-CD, with a bridging effect, is linked to the carboxylation CEA-aptamer 2* (Apt 2*) and BIBB via esterification reaction and substitution reaction, respectively. Remarkably, the combination of β-CD and the initiators BIBB can provide a large number of active sites for monomers and significantly amplify the fluorescent signal. Under optimum experimental conditions, the proposed biosensor for detecting CEA has a strong linear relationship in the wide detection range of 1.0 × 10−15–1.0 × 10−7 g mL−1 (R2 = 0.9989), and it is capable of detecting as low as 6.76 ag mL−1 CEA. Furthermore, the fluorescence biosensor exhibits splendid analytical performance in practical sample analysis. More importantly, the excellent sensitivity with outstanding anti-interference properties of this proposed biosensor makes it of great potential in the field of bioanalytical applications. [ABSTRACT FROM AUTHOR]

A fluorescence ratio sensor based on dansyl-peptide, Dansyl-Glu-Cys-Glu-Glu-Trp-NH2 (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. The sensor exhibits high selectivity and sensitivity for Ag+ over 16 metal ions in 100 mM sodium perchlorate and 50 mM 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid buffer solution by fluorescence resonance energy transfer. The 1:1 binding stoichiometry of the sensor and Ag+ is measured by fluorescence ratio response and the job's plot. The dissociation constant of the sensor with Ag+ was calculated to be 6.4 × 10−9 M, which indicates that the sensor has an effective binding affinity for Ag+. In addition, the limit of detection of the sensor for Ag+ was determined to be 80 nM, which also indicates that the sensor has a high sensitivity to Ag+. Result showed that the sensor is an excellent Ag+ sensor under neutral condition. Furthermore, this sensor displays good practicality for Ag+ detection in river water samples without performing tedious sample pretreatment, as well as for silver chloride detection. [ABSTRACT FROM AUTHOR]

A new Schiff base fluorescent probe, (E)-2-(2-hydroxybenzylidene) hydrazine-1-carboxamid (L), was synthesized and it exhibited solvent-directed high selectivity and sensitivity for Cu2+ and Mg2+ detections. Further, the interactions of L with Cu2+ and Mg2+ were investigated by Job's plot analysis, NMR, IR and XPS. [Display omitted] • A solvent-directed Schiff base fluorescent probe was synthesized. • The probe displayed excellent selectivity and sensitivity for Cu2+ in PBS buffer. • The probe displayed excellent selectivity and sensitivity for Mg2+ in acetonitrile. • The interactions of probe with Cu2+ and Mg2+ were characterized by NMR, IR and XPS. A solvent-directed, new Schiff base multiple correspondence fluorescent probe, (E)-2-(2-hydroxybenzylidene) hydrazine-1-carboxamid (L), was synthesized for selective sensing of Cu2+ and Mg2+ ions. L showed excellent selectivity and high sensitivity toward Cu2+ in "turn off" mode with a detection limit of 40.5 nM in 10 mM, pH = 7.0 PBS buffer. Contrary to that, when acetonitrile was used as the solvent, L exhibited highly selective and sensitive fluorescence sensing ability for Mg2+ in "turn on" mode with a detection limit of 9.5 nM. L can coordinate to Cu2+ and Mg2+ in a 1:1 molar ratio, respectively, evidenced by Job's plot analysis. Their binding modes were investigated by NMR, IR and XPS spectroscopies. Moreover, the satisfied results were obtained when L was used to detect Cu2+ and Mg2+ in real water samples. [ABSTRACT FROM AUTHOR]

The development of a convenient and efficient assay using miRNA-21 as a lung cancer marker is of great importance for the early prevention of cancer. Herein, an electrochemical biosensor for the detection of miRNA-21 was successfully fabricated under blue light excitation using click chemistry and photocatalytic atom transfer radical polymerization (photo-ATRP). By using hairpin DNA as a recognition probe, the electrochemical sensor deposits numerous electroactive monomers (ferrocenylmethyl methacrylate) on the electrode surface under the reaction of photocatalyst (fluorescein) and pentamethyldiethylenetriamine, thereby achieving signal amplification. This biosensor is sensitive, precise and selective for miRNA-21, and is highly specific for RNAs with different base mismatches. Under optimal conditions, the biosensor showed a linear relationship in the range of 10 fM ∼1 nM (R2 = 0.995), with a detection limit of 1.35 fM. Furthermore, the biosensor exhibits anti-interference performance when analyzing RNAs in serum samples. The biosensor is based on green chemistry and has the advantages of low cost, specificity and anti-interference ability, providing economic benefits while achieving detection objectives, which makes it highly promising for the analysis of complex samples. [Display omitted] • A miRNA-21 sensor based on atom transfer radical polymerization was designed. • Photo-ATRP based on catalyst fluorescein was first applied in biosensor. • The biosensor has highly sensitive to miRNA-21 with a detection limit of 1.35 fM. • The biosensor has good anti-interference ability in normal human serum. [ABSTRACT FROM AUTHOR]

An electrochemiluminescence approach based on surface-initiated reversible addition–fragmentation chain transfer (SI-RAFT) was developed for miRNA-21 detection for the first time. The SI-RAFT polymerization generates polymer chains with functional groups that are used to recruit luminol, enabling strong ECL signal output with low concentrations of miRNA-21, and greatly improving the detection sensitivity. [ABSTRACT FROM AUTHOR]

A fast and simple strategy for the detection of DNA based on a new type of electrochemical Zr(IV) signaling probe is reported. Briefly, this DNA biosensor was fabricated by covalently coupling the amino groups of peptide nucleic acid (PNA) probes with aldehyde groups on the surface of a glassy carbon electrode (GCE), for specifically capturing target DNA (tDNA). After this, Zr(IV) probes were attached to the phosphate groups of DNA directly with strong coordination interaction, and stoichiometrically labeled Zr(IV) probes can be detected via differential pulse voltammetry (DPV). Under optimized conditions, this strategy showed a good linear response from 0.01 nM to 100 nM tDNA, and the detection limit was 0.81 pM (R2 = 0.998). Moreover, this DNA biosensor is also successfully applied to the DNA detection in serum samples with satisfactory results and shows great potential in clinical analysis. [ABSTRACT FROM AUTHOR]

In this work, a new method of CYFRA21-1 DNA (tDNA) detection based on electrochemically mediated atom transfer radical polymerization (e-ATRP) and surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) cascade polymerization and AgNP deposition is proposed. Firstly, the peptide nucleic acid (PNA) probe is captured on a gold electrode by Au-S bonds for specific recognition of tDNA. After hybridization, PNA/DNA strands provide high-density phosphate groups for the subsequent ATRP initiator by the identified carboxylate-Zr4+-phosphate chemistry. Then, a large number of monomers are successfully grafted from the DNA through the e-ATRP reaction. After that, the chain transfer agent of SI-RAFT and methacrylic acid (MAA) are connected by recognized carboxylate-Zr4+-carboxylate chemistry. Subsequently, through SI-RAFT, the resulting polymer introduces numerous aldehyde groups, which could deposit many AgNPs on tDNA through silver mirror reaction, causing significant amplification of the electrochemical signal. Under optimal conditions, this designed method exhibits a low detection limit of 0.487 aM. Moreover, the method enables us to detect DNA at the level of PCR-like and shows high selectivity and strong anti-interference ability in the presence of serum. It suggests that this new sensing signal amplification technology exhibits excellent potential of application in the early diagnosis of non-small cell lung cancer (NSCLC). [ABSTRACT FROM AUTHOR]

In this paper, an ultrasensitive, highly selective and green electrochemical biosensor for quantifying DNA sequences (aM DNA) based on a MnTBAP catalyst for AGET ATRP reaction is proposed. For the first time, a combination of biomimetic catalyzed free radical polymerization and DNA electrochemical biosensing was used as a signal amplification strategy. [ABSTRACT FROM AUTHOR]

An ultrasensitive fluorescence biosensor for detecting cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA of non-small cell lung carcinoma (NSCLC) is designed using polysaccharide and activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) signal amplification strategy. Thiolated peptide nucleic acid (PNA) is fixed on magnetic nanoparticles (MNPs) by a cross-linking agent and hybridized with CYFRA 21-1 DNA. Hyaluronic acid (HA) is linked to PNA/tDNA heteroduplexes in the form of carboxy-Zr4+-phosphate. Subsequently, multiple 2-bromo-2-methylpropionic acid (BMP) molecules are linked with HA to initiate ARGET ATRP reaction. Finally, a large number of fluorescein o-acrylate (FA) monomers are polymerized on the macro-initiators, and the fluorescence signal is significantly amplified. Under optimal conditions, this biosensor shows a significant linear correlation between the fluorescence intensity and logarithm of CYFRA 21-1 DNA concentration (0.1 fM to 0.1 nM), and the limit of detection is as low as 78 aM. Furthermore, the sensor has a good ability to detect CYFRA 21-1 DNA in serum samples and to recognize mismatched bases. It suggests that the strategy has broad application in early diagnosis by virtue of its high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

An ultrasensitive fluorescence method for early diagnosis of lung cancer via activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) with EDTA as metal ligand was reported. In this paper, we reported a system for the ultrasensitive fluorescence detection of cytokeratin fragment antigen 21–1 DNA (CYFRA21-1 DNA) for the early diagnosis of lung cancer. The approach used electron transfer atom transfer radical polymerization (ARGET-ATRP) with ethylenediaminetetraacetic acid (EDTA) as the metal ligand. Firstly, thiolated peptide nucleic acid (PNA) was linked to aminated magnetic beads solutions (MBs) by a cross-linking agent and then hybridized with CYFRA21-1 DNA (tDNA). Subsequently, Zr4+ was introduced into the MBs by conjugating with the phosphate group of tDNA, and the initiator of ARGET-ATRP was introduced into via phosphate-Zr4+-carboxylate chemistry. Next, Cu(II)Br/EDTA was reduced to Cu(I)/EDTA by ascorbic acid (AA) to trigger ARGET-ATRP and then a large amount of fluorescein-o-acrylate (FA) molecules were grafted from the surface of the MBs, which amplified significantly the fluorescent signal. Under optimal conditions, a strong linear relationship of tDNA over the range from 0.1 fM to 1 nM (R2 = 0.9988). The limit of detection was as low as 23.8 aM (~143 molecules). The fluorescence detection based on the ARGET-ATRP strategy yielded excellent sensitivity, selectivity, outstanding anti-interference properties, and cost-effectiveness. These results indicated that this strategy has considerable potential for biological detection and early clinical diagnosis. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensor was reported for the first time to achieve highly sensitive DNA detection based on photoinduced atom transfer radical polymerization (photoATRP). In this work, PNA was applied as the capture probe to specifically recognize the target DNA (TDNA), and we utilized lung cancer DNA as TDNA. The ATRP initiator was introduced to the electrode surface via phosphate-Zr4+-carboxylate chemistry. PhotoATRP was activated under blue light irradiation based on a photoinitiator I2959, which produced free radicals via homolytic cleavage. Subsequently, Cu2+ was reduced to Cu+ with the assistance of the free radicals, and numerous electroactive probes were grafted onto the electrode surface. Under optimal conditions, the limit of detection (LOD) of this method was 3.16 fM (S/N = 3, R2 = 0.992), and the linear range was from 10 fM to 1.0 nM. More importantly, the preparation process of this biosensor was simple and less laborious with a low background signal, suggesting good potential in practical applications. [ABSTRACT FROM AUTHOR]

Convenient and sensitive detection of biomolecules is of great significance to disease diagnosis. In this work, a metal‐free photoinduced atom transfer radical polymerization (photoATRP) by a reductive quenching pathway as a novel strategy is applied to achieve lung cancer DNA detection. Thiolated PNA is exploited to specifically recognize target DNA, and the initiator of photoATRP is linked to the electrode surface via phosphate‐Zr4+‐carboxylate. Under the excitation of blue light, the reductive quenching pathway is activated with eosin Y (EY) as photoredox catalyst and N,N,N′,N′′,N′‐pentamethyldiethylenetriamine (PMDETA) as electron donor, and numerous polymeric chains are formed. Under optimal conditions, the linear range of this strategy is from 0.1 pm to 10 nm (R2=0.989) with a limit of detection (LOD) of 1.4 fm (14 zmol in 10 μL). The variety of possible light sources for photoATRP and simple operation endow this biosensor with great potential for practical applications. [ABSTRACT FROM AUTHOR]

In this study, poly(3,4‐ethylenedioxythiophene) (PEDOT) and polyaniline (PANI) were electrodeposited via cyclic voltammetry (CV) on glass carbon electrode (GCE) layer by layer. The prepared electrode (GCE/PEDOT/PANI) was used for the simultaneous sensitive determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) at different oxidation potentials. The peak distances of AA and DA, DA and UA, AA and UA were 216 mV, 104 mV, 320 mV, respectively. For individual detection of AA, DA and UA, the linear ranges were 1×10−4‐1×10−2 M, 3×10−5‐1×10−3 M and 7×10−7‐1×10−4 M with detection limits of 2.42×10−5 M, 4.58×10−6 M and 2.38×10−7 M (S/N=3), respectively. For simultaneous detection of AA, DA, and UA, the linear response ranges were 1×10−4‐1×10−3 M, 3×10−4‐1×10−2 M, and 3×10−6‐1×10−4 M with detection limits of 6.91×10−5 M, 3.66×10−5 M and 4.13×10−7 M (S/N=3), respectively. The GCE/PEDOT/PANI displayed good selectivity, reproducibility and storage stability, and was further applied to the detection of AA, DA, and UA in 5% normal human serum samples. [ABSTRACT FROM AUTHOR]

An ultrasensitive fluorescence method for early diagnosis of lung cancer via Nafion-initiated atom transfer radical polymerization (ATRP) is reported, in this paper. In the proposed method, thiolated peptide nucleic acid (PNA) is modified to amino magnetic beads (MBs) via a cross-linking agent to specifically capture target DNA (tDNA), and the initiator (Nafion) of ATRP is attached to PNA/DNA heteroduplexes based on the phosphate groups of the tDNA and sulfonate groups of Nafion via phosphate-Zr4+-sulfonate chemistry. Nafion as a macroinitiator of ATRP possesses multiple C–F active sites to initiate polymerization, and numerous polymeric chains that significantly amplify the fluorescent signal are formed. Under optimal conditions, a good linear relationship is obtained in the range of 0.1 nM–0.1 fM with correlation coefficients of 0.9975, and the detection limit is as low as 35.5 aM (∼214 molecules). The proposed strategy has several advantages of simplicity, cost-effectiveness, selectivity and sensitivity. More importantly, the anti-interference results demonstrate that the proposed Nafion-initiated ATRP strategy has great potential in bioanalytical applications. An ultrasensitive fluorescence method for early diagnosis of lung cancer via Nafion-initiated atom transfer radical polymerization (ATRP) was reported. Image 1 • Nafion, as the initiator, has multiple active sites to generate free radical and can bind more monomers. • A novel DNA detection for early diagnosis of lung cancer based on Nafion-initiated ATRP was reported for the first time. • This detection has a fairly simple, gentle, cost-effectiveness process with high selectivity and interference immunity. [ABSTRACT FROM AUTHOR]

A highly sensitive method is described for determination of DNA. It is based on dual signal amplification, viz. (a)DNA-templated metal deposition, and (b) thermally initiated surface-initiated reversible addition−fragmentation chain transfer (SI-RAFT) polymerization. A peptide nucleic acid (PNA) with a terminal thiol group was grasped onto a gold electrode by self-assembly. The modified electrode serves as a probe to selectively capture target DNA (tDNA). In the next step, Zr(IV) ions are bound to the phosphate groups of the tDNA. A chain-transfer agent (CTA) for thermally initiated SI-RAFT polymerization, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD), was immobilized on tDNA by conjugation of the carboxy group to Zr(IV) ions. Subsequently, numerous monomers of glycosyloxyethyl methacrylate (GEMA) were connected to the CPAD by thermally initiated SI-RAFT polymerization with azobisisobutyronitrile (AIBN) serving as the free-radical thermal initiator. Afterwards, hydroxyl groups of the GEMA were oxidized to aldehyde groups reacting with sodium periodate, and silver nanoparticles were further introduced on the surface of electrode via "silver mirror reaction". This results in a large electrochemical signal amplification. Under optimized conditions, the electrochemical signal (best measured at a working potential of 0 V vs. SCE (KCl; 3 M)) increases linearly with the logarithm of tDNA concentration in the 10 to 106 aM concentration range. The detection limit is as low as 5.6 aM (~34 molecules in a 10 μL sample). This is lower by factors between 2 and 1800 times than detection limits of most other ultra-sensitive electrochemical DNA assays. [ABSTRACT FROM AUTHOR]

Sensitive detection of DNA is conducive to enhance the accuracy of diseases diagnosis and risk prediction. In this work, we report the use of activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) as a novel on-chip amplification strategy for the fluorescence detection of DNA. More specifically, the target DNA was captured by the on-chip immobilized hairpin DNA probes. Upon hybridization, exposed 3′-N 3 of the hairpin was used to attach AGET ATRP initiators onto the silicon surface by click chemistry. Then, numerous fluorescent labeling linked to the end of the probes via the formation of long chain polymers of fluorescein o-acrylate, which in turn amplified the fluorescence signal for DNA detection. Under optimal conditions, it showed a good linear range from 100 fM to 1 μM in DNA detection, with the limit of detection as low as 4.3 fM. Moreover, this strategy showed good detection performance in complex real serum samples, the fluorescence intensity of 0.1 nM tDNA in 1% fetal bovine serum samples was 97.6% of that in Tris-EDTA buffer. Based on its high sensitivity, reduced cost and simplicity, the proposed signal amplification strategy displays translational potential in clinical application. Image 1 • Labeling hairpin DNA probes for fluorescence polymers can amplify DNA signals. • The linear range of the method is 100 fM to 1 μM, and the detection limit is 4.3 fM. • The strategy can distinguish single base mismatches of DNA. • The strategy showed good detection capability in serum samples. [ABSTRACT FROM AUTHOR]

Given the gigantic harmfulness of bisphenol A (BPA), a novel and ultrasensitive aptasensor, which employs the truncated BPA aptamer, click chemistry, and activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP), was developed herein for the quantitative determination of BPA. Firstly, hairpin DNAs (hairpins) with a thiol at the 5′ end and an azide group at the 3′ end were conjugated with aminated magnetic beads (MBs) through heterobifunctional cross-linkers. BPA truncated aptamer (ssDNA-A) hybridizes with its complementary single-stranded DNA (ssDNA-B) to form double-stranded DNA. In the presence of BPA, ssDNA-A specifically captures BPA, and then ssDNA-B is released. Subsequently, the ssDNA-B hybridizes with hairpins to expose the azide group near the surface of the MBs. Then, propargyl-2-bromoisobutyrate (PBIB), the initiator of AGET ATRP containing alkynyl group, was conjugated with azide group of hairpins via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Consequently, a large number of fluorescein-o-acrylate (FA) were introduced to the MBs through AGET ATRP, resulting in that the fluorescence intensity was increased dramatically. Obviously, the fluorescence intensity was especially sensitive to the change of BPA concentration, and this method can be used in quantitative determination of BPA. Under optimal conditions, a broad liner range from 100 fM to 100 nM and a low limit of detection (LOD) of 6.6 fM were obtained. Moreover, the method exhibits not only excellent specificity for BPA detection over BPA analogues but high anti-interference ability in real water sample detection, indicating that it has huge application prospect in food safety and environment monitoring. [ABSTRACT FROM AUTHOR]

Herein, a novel aptasensor was constructed for ultrasensitive detection of bisphenol A (BPA). In this method, an electrochemically mediated atom transfer radical polymerization (eATRP) signal amplification strategy was applied to BPA detection for the first time. The 5′-end modified sulfhydryl group and the 3′-end modified azide group hairpin DNA were immobilized on a gold electrode through an Au–S bond. The double-stranded DNA was formed by the hybridization of an aptamer and a single-stranded DNA partially paired with the hairpin DNA. In the presence of BPA, the aptamer combined with BPA and the single-stranded DNA was released to open the hairpin structure, making the azide groups at the 3′ end exposed. Subsequently the initiator of eATRP was introduced into hairpin DNA through click chemistry reaction and eATRP was conducted for the polymerization of the electroactive probe ferrocene methyl methacrylate (FMMA). As a result, the ultrasensitive detection of BPA was realized, and the detection limit of this aptasensor was as low as 59 aM and a good selectivity was obtained in the presence of 100-fold structural analogs. The application of this aptasensor was evaluated by detecting BPA in pure water samples, and recoveries were in the range of 95.23–98.40%, holding promising applications in biological analysis. [ABSTRACT FROM AUTHOR]

Ultrasensitive aptamer fluorometric detection of gamma-interferon by dual ATRP amplification. • A new aptamer fluorometric protein sensor was fabricated by dual ATRP amplification. • This supersandwich fluorescence method has great potential in realize ultrasensitive protein (IFN-γ) detection in human serum. • This novel preparation is simple, gentle and convenient. Exploiting biological detection methods with high selectivity and sensitivity has been an urgent demand for low abundance biomolecules. Herein, an ultrasensitive aptamer fluorometric method of protein detection was fabricated via a sequential dual atom transfer radical polymerization (ATRP). For the first time, surface-initiated dual ATRP was utilized to make the fluorometric signal amplification for gamma-interferon (IFN- γ) protein assay. Two aptamers are used as protein probes, which can form a high stable and selective "aptamer/ protein/aptamer" sandwich structure. One aptamer probe is attached on superparamagnetic nanoparticle via surface self-assembled, the other one is linked with initiators of dual ATRP amplification by click chemistry formed triazole group. With large numbers of fluorescein-o-acrylate grown directly on a nanoparticle surface, a convenient "aptamer/protein/aptamer-polymer" supersandwich sensor was fabricated. Under optimal conditions, IFN- γ can be assayed with detection limit down to 0.178 fM in PBS buffer (equals to 1.072 ˣ103 IFN-γ molecules). Even in complex human serum, IFN-γ can also be detected with the limit of 1.54 fM, equals to 9.275 ˣ103 IFN-γ molecules. Results show a great potential in real ultrasensitive protein detection for its high selectivity, efficiency and stability. Besides, this proposed sensing method, which combines the advantages of superparamagnetic nanomaterial and chemically catalyzed surface-initiated dual ATRP polymerization, compared to the traditional signal amplify methods, is novel, more convenient, simpler and enzyme-free cascade amplification. [ABSTRACT FROM AUTHOR]

Abstract A novel, simple, and label-free amplification electrochemical impedance method for quantitative detection of Human T-lymphotropic virus types II(HTLV-II) via click chemistry-mediated of hairpin DNA probes (hairpins) with polymers was developed. The hairpins were firstly attached to the gold electrode surface by an S-Au bond, the azido terminals of hairpins were close to the electrode surface, which make it difficult to be approached. After hybridizing with HTLV-II, the hairpins were unfolded and experienced a big configuration change, which made the azido terminals of the hairpins available to conjugate with alkynyl-containing polymer, called P(DEB-DSDA), formed by 1,4-diacetylenebenzene (DEB) and 4,4′-Diazido-2,2′-stilbenedisulfonic acid disodium salt tetrahydrate (DSDA) via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). With amount of P(DEB-DSDA) conjugated with the hairpin probes via click polymerization, its electrochemical signal can have a great amplification. Under optimized experimental conditions, this new probe showed a low detection limit of 0.171 pM with a good liner in the range of 1 pM-1 nM. Meanwhile, the biosensor also exhibited good selectivity and reliability in detection of real serum samples, indicating that it has great application potential in clinical DNA diagnosis and detection. Graphical abstract A novel, simple, and label-free amplification electrochemical impedance method for quantitative detection of Human T-lymphotropic virus types II via click chemistry-mediated of hairpin DNA probes (hairpins) with polymers was developed. Image 1 Highlights • In absence of enzymes and nanomaterials, a novel and label-free amplification electrochemical impedance technique for the detection of HTLV-II was developed. • The DNA detection based on click-chemistry EIS amplification has considerable simplicity, label-free, cheap "green" process, highly selective and flexibility with respect to reporter design. [ABSTRACT FROM AUTHOR]

Abstract Here we report a highly selective and ultrasensitive DNA biosensor based on electrochemical atom transfer radical polymerization (ATRP) signal amplification and "Click Chemistry". The DNA biosensor was prepared by immobilizing thiol and azide modified hairpin DNAs on gold electrode surface. In the presence of target DNAs (T-DNA), hairpin probes hybridized with T-DNAs to form a duplex DNA, and the ring of hairpin DNA was opened to make azide groups accessible at 3′ ends. "Click reactions" proceeded between the azide and propargyl-2-bromoisobutyrate (PBIB) to initiate the ATRP reaction which brought a large number of ferrocenylmethyl methacrylate (FMMA) on the electrode surface. The amount of FMMA was proportional to the concentration of T-DNA and quantified by square wave voltammetry. Combining ATRP signal amplification with "Click Chemistry", the optimized DNA biosensor was capable of detecting 0.2 aM. T-DNA. The preliminary application of the developed DNA biosensor was demonstrated by detecting target DNA in spiked serum samples. The developed DNA biosensor shows great promise for the detection of gene biomarkers. Highlights • A highly selective and ultrasensitive DNA detection method was developed by utilizing electrochemical atom transfer radical polymerization (ATRP) signal amplification and click chemistry. • The optimized biosensor was capable of detecting 0.2 aM target DNA. • This signal amplification strategy can be applied for the detection of protein and other biological molecular. [ABSTRACT FROM AUTHOR]

In view of the vital role of biothiols in many physiological processes, the development of simple and efficient probe for the detection of biothiols is of great medical significance. In this work, we demonstrate the use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), which respond rapidly to biothiols especially to glutathione, as a new fluorescent probe for the selective detection and bioimaging of biothiols. This new fluorescent probe can distinguish glutathione from cysteine and homocysteine easily under physiological concentration and detect glutathione quickly within three minutes. This probe exhibits high selectivity to biothiols and the detection limit was determined to be 3.08 × 10−9 M for glutathione, 8.55 × 10−8 M for cysteine, and 2.17 × 10−9 M for homocysteine, respectively. The sensing mechanism was further explored by density functional theory (DFT) and nuclear magnetic resonance (NMR) experiment; results showed that the interaction forces between the probe and biothiols were electrostatic interaction. In addition, the probe has been successfully applied to the detection of biothiols in Eca9706 cells by fluorescence confocal imaging technology. [ABSTRACT FROM AUTHOR]