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Precise and spatiotemporally controllable analysis of microRNA-21 in living cells is crucial for accurate diagnosis and effective treatment of related diseases. Herein, a near-infrared (NIR)-photoactivatable DNA nanomachine (PUCNPs-NH 2 /PEG-ZL-DNA) was constructed for the precise analysis and diagnosis of microRNA-21 in tumor cells. Peanut-shaped upconversion nanoparticles (PUCNPs) were employed as the carriers and activators for the intelligent DNA probe, specifically enabling the cleavage of the photocleavable linker (PC-linker) from the hairpin DNA probe (Hp-Dzy) upon exposure to 808 nm irradiation. In the presence of the target microRNA-21, the locker DNA hybridized with microRNA-21 and the DNAzymes was freed to hybridize with the looped portion of the hairpin DNA (Hp-1). Mg 2+ was employed as the cofactor, facilitating the precise cleavage of Hp-1, which triggered the restoration of fluorescence signals. Subsequently, DNAzymes exhibited the competency to selectively recognize and engage with additional Hp-1, and the fluorescence signals were effectively amplified by the recycling process. Consequently, the DNA nanomachine exhibited a linear response to microRNA-21 concentrations ranging from 0.5 nM to 1.0 μM, achieving a remarkable detection limit (LOD) of 1.19 nM under the optimal conditions. This strategy is realized through the integration of photocontrollable upconversion nanotechnology with the signal amplification approach, showing feasible prospects for spatiotemporally precise and highly sensitive monitoring of microRNA in tumor cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Hydrogels, water-filled networks that can adapt to external stimuli by altering their volume, are known for their high flexibility and biocompatibility. DNA, a critical biomolecule renowned for its exceptional characteristics including information transmission, molecular recognition, and editability, has found widespread applications in the biosensing field as well. The integration of these two biomaterials offers promising opportunities for the development of novel biosensors with enhanced sensitivity, specificity, and adaptability. Therefore, by virtue of the collective features, researchers have recently focused on the construction of responsive DNA hydrogel systems. This feature article describes recent developments in fabricating DNA hydrogels and their applications in the biosensing area. Initially, it focuses on the design strategies employed in preparing DNA hydrogels, encompassing both pure DNA hydrogels and hybridized DNA hydrogels. Subsequently, it summarizes the use of DNA hydrogels in biosensing applications, highlighting their applications in visual detection, electrochemical sensing, and optical biosensing analyses. Furthermore, the underlying responsive mechanisms within these biosensing systems are also described. Lastly, this article presents a comprehensive discussion on the existing challenges and prospects of responsive DNA hydrogels, offering insights into their potential to revolutionize the field of biosensing.

In electrochemical analysis, developing biosensors that can resist the nonspecific adsorption of interfering biomolecules in human serum remains a huge challenge, which depends on the design of efficient antifouling materials. Herein, 3-aminopropyldimethylamine oxide (APDMAO) biomimetic zwitterions were prepared as antifouling interfaces. Among them, the unique positive and negative charges (N + -O - ) of APDMAO promoted its hydrogen bonding with water molecules, forming a firm hydration barrier that endowed it with strong and stable antifouling performance. Meanwhile, its inherent amino groups could copolymerize with the biomimetic adhesive dopamine to form a thin layer of quinone intermediates, providing conditions for the subsequent binding of aptamers and signal probes. Importantly, the biomimetic APDMAO with functional groups and one-step oxidation characteristics solved the challenges of zwitterionic synthesis and modification, as well as improved biocompatibility of the sensing interface, thereby expanding the application potential of zwitterions as antifouling materials in sensing analysis. Thiol-containing alpha-fetoprotein (AFP) aptamers modified with methylene blue (MB) were coupled under controllable potential, greatly reducing the incubation time, which promoted the productization application of biosensors. In addition, the ratio sensing strategy using MB as internal standard factors and concanavalin-silver nanoparticles (ConA-Ag NPs) as signal probes was introduced to reduce background and instrument interferences, thus improving detection accuracy. On this basis, the proposed antifouling electrochemical biosensor achieved sensitive and accurate AFP detection over a wide dynamic range (10 fg/mL-10 ng/mL), with a low detection limit of 3.41 fg/mL (3σ/ m ). This work provides positive insights into the development of zwitterionic antifouling materials and clinical detection of liver cancer markers in human serum.

In this study, a novel antifouling electrochemiluminescence (ECL) analytical platform has been developed for the highly sensitive quantification of β-amyloid (Aβ) peptides based on the ECL resonance energy transfer (ECL-RET) mechanism. Specifically, glassy carbon electrodes (GCE) were initially coated with graphite-phase carbon nitride (g-C 3 N 4 ) nanosheets, followed by the electropolymerization of polyaniline (PANI) onto the electrode surface. Subsequently, a promising peptide motif candidate (COOH-CPPPPDKDKDKDKKLVFF) was immobilized onto the PANI-modified electrode, functioning as a critical component for both antifouling and specific recognition of full-length Aβ peptides. Furthermore, this peptide motif demonstrated inhibitory effects on Aβ aggregation and dissociation. Upon immobilization of the peptide motif, Aβ aptamer-CdS QDs were bound to the electrode surface through peptide-specific interactions with Aβ, thereby facilitating the highly sensitive ECL detection of Aβ. Under the optimal conditions, the proposed biosensor exhibited an Aβ detection range from 0.1 pM to 100 nM with a detection limit of 16.1 fM. As such, this innovative platform offers a straightforward approach to antifouling, quantification, and monitoring of Aβ concentrations in the blood samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Developing a generalized strategy for the nonfouling detection of biomarkers in diverse biological fluids presents a significant challenge. Herein, a polyhydroxyproline helical peptide (PHHP) was designed and adopted to fabricate electrochemical microsensors capable of detecting targets in various biological media. The PHHP possessed unique properties such as strong hydrophilicity, rigid structure, and lack of ionizable side-chain groups. Compared with common zwitterionic peptides (ZIPs), the PHHP exhibited similar antifouling capability but exceptional stability, allowing its antifouling performance to be unaffected by environmental alteration. The PHHP can prevent biofouling even in fluctuating pH conditions, high ionic strength environments, and the presence of high-valence ions and resist the protease hydrolysis. The PHHP-modified carbon fiber microelectrode was further immobilized with an aptamer to construct an antifouling microsensor for cortisol detection across diverse biofluids, and the microsensor exhibited acceptable accuracy and higher sensitivity than the ELISA method. In addition, different biological samples of mice were collected in situ using a microsensing device, and cortisol levels were analyzed in each specifically tailored region. This nonfouling sensing strategy based on PHHP allows a comprehensive assessment of biomarkers in both spatial and temporal dimensions in diverse biological environments, holding promising potential for early disease diagnosis and real-time health monitoring.

Based on the designed inverted Y-shaped peptide and MXene nanocomposite (MXene-Au@ZIF-67), a ratiometric anti-pollution electrochemical biosensor was designed and applied to the detection of biomarkers in serum. Au@ZIF-67 inserted into the interior of MXene can not only prevent the accumulation of MXene but also provide a large amounts of binding sites for capturing biomolecules. A designed multifunctional Y-shaped peptide containing anchoring, antifouling, and recognition sequences was anchored onto MXene-Au@ZIF-67 through Au-S bonds. Electrochemical signal molecules, ferrocenecarboxylic acid (Fc) and methylene blue (MB), were modified to another end of multifunctional peptide and interior of MXene-Au@ZIF-67, respectively, to produce a ratiometric electrochemical signal. We selected prostate specific antigen (PSA) as the model compound. PSA specifically recognizes and cleaves the recognition segment in the Y-shaped peptide, and the signal of Fc is reduced, while the signal of MB remains unchanged. The ratiometric strategy endows the present biosensor high accuracy and sensitivity with a detection limit of 0.85 pg/mL. In addition, the sensing surface has good antifouling ability due to the antifouling sequence of the two branching parts of the Y-shaped peptide. More importantly, by replacing the recognition segment of peptides also other targets are accessible, indicating the potential application of the universal detection strategy to the detection of various biomarkers in clinical diagnosis., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The sensitivity and accuracy of electrochemiluminescence (ECL) sensors for detecting small-molecule pollutants in environmental water are affected not only by nonspecific adsorption of proteins and other molecules but also by bacterial interference. Therefore, there is an urgent need to develop an ECL sensor with antifouling and antibacterial functions for water environment monitoring. Herein, a highly efficient antifouling sensing interface (PSBMA@SiO 2 -MXene) based on zwitterionic sulfobetaine methacrylate (SBMA) antifouling nanospheres (NPs) and two-dimensional MXene nanosheets was designed for the sensitive detection of oxytetracycline (OTC), an antibiotic small-molecule pollutant. Specifically, SBMA with good hydrophilicity and electrical neutrality was connected to SiO 2 NPs, thus effectively reducing protein and bacterial adsorption and improving stability. Second, MXene with a high specific surface area was selected as the carrier to load more antifouling NPs, which greatly improves the antifouling performance. Meanwhile, the introduction of MXene also enhances the conductivity of the antifouling interface. In addition, a ratio-based sensing strategy was designed to further improve the detection accuracy and sensitivity of the sensor by utilizing Au@luminol as an internal standard factor. Based on antifouling and antibacterial interfaces, as well as internal standard and ratiometric sensing strategies, the detection range of the proposed sensor was 0.1 ng/mL to 100 μg/mL, with a detection limit of 0.023 ng/mL, achieving trace dynamic monitoring of antibiotics in complex aqueous media.

It is difficult to show microbial growth kinetics online when they grow in complex matrices. We presented a novel strategy to address this challenge by developing a high-performance microbial growth analyzer (HPMGA), which employed a unique 32-channel capacitively coupled contactless conductivity detector as a sensing element and fixed with a CellStatz software. It was capable of online showing accurate and repeatable growth curves of well-dispersed and bad-dispersed microbes, whether they grew in homogeneous simple culture broth or heterogeneous complex matrices. Moreover, it could automatically report key growth kinetics parameters. In comparison to optical density (OD), plate counting and broth microdilution (BMD) methods, we demonstrated its practicability in five scenarios: 1) the illustration of the growth, growth rate, and acceleration curves of Escherichia coli (E. coli); 2) the antimicrobial susceptibility testing (AST) of Oxacillin against Staphylococcus aureus (S. aureus); 3) the determination of Ag nanoparticle toxicity on Providencia rettgeri (P. rettgeri); 4) the characterization of milk fermentation; and 5) the enumeration of viable pathogenic Vibrio in shrimp body. Results highlighted that the HPMGA method had the advantages of universality and effectivity. This technology would significantly facilitate the routine analysis of microbial growth in many fields (biology, medicine, clinic, life, food, environment, and ecology), paving an avenue for microbiologists to achieve research goals that have been inhibited for years due to a lack of practical analytical methods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Specific peptide-protein interactions play an important role in biosensing systems based on functional peptides; however, the non-specific interactions with unrelated biomolecules and poor proteolytic stability restrict the clinical application of natural peptides. Here, we leveraged a self-designed multifunctional isopeptide (MISP) to construct an electrochemical biosensing platform for annexin A1 (ANXA1) detection in human blood. The MISP was designed to contain two parts: an antifouling cyclotide cyclo-C(EK) 4 and a d-amino acid-containing carbohydrate-mimetic recognizing peptide IF-7 (D-IF7) connected by the isopeptide bond. We have discussed the properties of the cyclotide and illustrated its unique advantage over the natural linear antifouling peptides by molecular dynamics simulations, and the results were further confirmed by dissipative quartz crystal microbalance (QCM-D). In addition, through electrochemical experiments and fluorescence imaging experiments, we demonstrated that the MISP-based biosensor possessed excellent antifouling ability and proteinase hydrolysis stability. Interestingly, the assaying results of the MISP-biosensor were consistent with those of the commercial ANXA1 kits in a variety of healthy and ANXA1-upregulated clinical blood samples, and, more importantly, for the analysis of blood samples with lower ANXA1 expressions, the sensing capability of the biosensor was greatly superior to that of the kits because of the lower detection limit of the MISP-biosensor. This biosensing platform based on the designed MISP offers enormous potential for achieving accurate biomarker detection with robust operation in complex biological samples.

Photocathodic immunosensors generally exhibit fortified anti-interference abilities than photoanodic ones against the detection in biological specimens. Yet, the weak photocurrent signals of the photocathodes have limited evidently the detection performance. Herein, an efficient and feasible photoelectrochemical (PEC) immunosensor was developed on the basis of the featured photocathode-photoanode operating system. In the proposal, the elaborated PEC immunosensor integrated photocathode with photoanode, and the immune recognition occurred just on the photocathode. To illustrate the performance, α-fetoprotein (AFP) was selected as a target antigen (Ag) for detection. TiO 2 nanoparticles were decorated with AgInS 2 quantum dots (AIS QDs) to fabricate the TiO 2 /AIS photoanode, and the carbon nanotubes (CNTs) were modified with CuInS 2 nanoflowers (CIS NFs) to prepare the CNT/CIS photocathode for the capture AFP antibody (Ab) anchoring. Target Ag detection depended on significant decrease of the photocurrent signal produced by large steric hindrance of the captured AFP molecules. Coupling excellent photoelectric property with anti-interference ability in this elegant PEC immunosensor, sensitive and specific probing of target Ag was realized. The proposed photocathode-photoanode integrating strategy provides a promising way to explore other high-performance PEC immunosensors against the detection in biological matrixes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

An antifouling sensing surface was constructed by crosslinking two-dimensional nanomaterial MXene with bovine serum albumin (BSA) denatured by urea previously. The immunoglobulin G (IgG) capture peptide was then modified to the surface to construct a highly selective antifouling electrochemical biosensor. Due to the large specific surface area and good electrical conductivity of MXene, the sensitivity of the biosensor is significantly enhanced. The biosensor at a working potential of around - 0.18 V (vs. Ag/AgCl) provides a wide linear detection range (0.1 ng/mL to 10 µg/mL) for IgG with a limit of detection of 23 pg/mL (3σ/k). The result is consistent with that obtained from the commercial enzyme-linked immunosorbent kit. Compared with BSA, which is usually used as a passivator or blocker for biosensing platforms, the hydrogel formed through the peptide chain obtained from BSA with good hydrophilicity can provide a better antifouling sensing surface to resist nonspecific adsorption. The prepared biosensor can quantitatively detect the concentration of IgG in complex human serum with high sensitivity. Thus, the antifouling sensing surface constructed without expensive antifouling materials and complex process is expected to develop as a variety of electrochemical biosensors and used for the clinical testing of biomarkers. Graphical abstract An antifouling sensing surface was constructed by crosslinking two-dimensional nanomaterial MXene with bovine serum albumin (BSA) denatured by urea previously. The immunoglobulin G (IgG) capture peptide was then modified to the surface to construct a highly selective antifouling electrochemical biosensor., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A novel ratio electrochemical biosensor based on multi-functional nanocomposite was developed. Fe 3 O 4 was synthesized in situ on carboxyl functionalized 2D nanomaterial MXene, and then covalently bonded with [Ru(NH 3 ) 6 ] 3+ to obtain nanocomposites MXC-Fe 3 O 4 -Ru. Fe 3 O 4 and [Ru(NH 3 ) 6 ] 3+ can neutralize the electronegativity of the MXene to make the nanocomposites electrically neutral. Combine with the good hydrophilicity and conductivity of MXene, the nanocomposites can be utilized to construct antifouling electrochemical biosensors without modifying with specific antifouling materials. Moreover, Fe 3 O 4 can endow the nanocomposites with magnetism, and [Ru(NH 3 ) 6 ] 3+ is used as an internal standard molecule. The strong magnetic MXC-Fe 3 O 4 -Ru can be easily separated and firmly modified on the magnetic gold electrode (MGE). DNA double-stranded (dsDNA) containing an ferrocene (Fc)-modified carcinoembryonic antigen (CEA) aptamer can be specifically captured to the surface of the electrode by amido bond. In the presence of CEA, CEA binds to the aptamer and leaves the electrode surface, the electrochemical signal of Fc decreases, while the electrochemical signal of [Ru(NH 3 ) 6 ] 3+ is fixed on the electrode surface remains basically unchanged. The ratio of the electrochemical signals of Fc and [Ru(NH 3 ) 6 ] 3+ is proportional to the CEA concentration. The linear range of the sensor is 1 pg/mL to 1 μg/mL with a detection limit of 0.62 pg/mL. With the excellent antifouling performance, good conductivity of the nanocomposite, and the application of the ratiometric strategy, the biosensor can achieve high selectivity, accuracy, and sensitivity for the detection of targets even in complex samples, such as FBS and clinical serum., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Target biomarker detection with high accuracy in biological sample is necessary for the constructed immunoassays. Herein, a novel and enhanced cathodic immunosensor supported by photoanode was designed for sensitive and specific detection of human chorionic gonadotropin (HCG). Specifically, the electrode of TiO 2 nanotube with N doping (TiO 2 :N) was fabricated and assembled with AgInS 2 quantum dots (QDs) to acquire the TiO 2 :N/AgInS 2 photoanode. For the sensing cathode, Pt nanoparticles (NPs) were decorated on carbon nanotubes (CNTs) to prepare the CNT/Pt cathodic matrix and was used to modify capture HCG antibody (Ab). In this photoelectrochemical (PEC) sensing system, the TiO 2 :N/AgInS 2 photoanode served as the signal-converting element to produce prominent current signal, while the immune recognition events occurred on the sensing cathode to evidently change the initial current signal from steric hindrance effect. Profiting by excellent photoelectric property and good anti-interference ability of this featured PEC system, the developed cathodic immunosensor demonstrated high sensitivity and specificity for the detection of target HCG antigen (Ag). This photoanode-supported cathodic sensing strategy provided a potential path forward to exploit other enhanced PEC immunosensors in the application of biological samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Circulating tumor cells (CTCs) are considered reliable cancer biomarkers for the liquid biopsy of many types of tumors. The direct detection of CTCs in human blood with normal biosensors, however, remains challenging because of severe biofouling in blood that contains various proteins and a large number of cells. Herein, we report the construction of an antifouling electrochemical biosensor capable of assaying CTCs directly in blood, based on a designed multifunctional peptide and the electrodeposited conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The designed peptide possesses antifouling capability in complex biological media and specific recognition ability to capture breast cancer cells MCF-7. Meanwhile, electrodeposited PEDOT can promote electron transfer at the sensing interface, improve the signal-to-noise ratio for the detection, and thus enhance the sensitivity of the biosensor. The integration of the multifunctional peptide and conducting polymer PEDOT ensures that the developed biosensor is able to perform directly in blood samples without purification or separation. The antifouling electrochemical biosensor for the detection of MCF-7 cells exhibits a wide linear range over 4 orders, with a limit of detection (LOD) of 17 cells mL -1 . More interestingly, even when performing in 25% human blood, the biosensor still retains a linear response with an LOD of 22 cells mL -1 , without suffering significantly from biofouling in real blood. This work provides a promising strategy for the direct analysis of CTCs in human blood without a complicated pretreatment, and it may find practical application in the liquid biopsy of cancers.

It is important to develop highly-active photoelectrochemical (PEC) materials and use novel sensing strategy for constructing high-PEC-performance sensors with multiplex detection abilities, owing to the simultaneous presence of multiple antibiotic residues in food. Herein, a bias-potential-based PEC aptasensor was prepared for the trace detection of dual antibiotic analytes, enrofloxacin (ENR) and ciprofloxacin (CIP), which often coexist in milk samples. Here, two materials were developed with excellent PEC performance: three-dimensional nitrogen-doped graphene-loaded copper indium disulfide (CuInS 2 /3DNG) and Bi 3+ -doped black anatase titania nanoparticles decorated with reduced graphene oxide (Bi 3+ /B-TiO 2 /rGO). By applying different bias potentials to the two materials near one ITO electrode, the cathodic current generated by CuInS 2 /3DNH and the anodic current generated by Bi 3+ /B-TiO 2 /rGO could be clearly distinguished without interfering with each other. Then, ENR and CIP aptamers were respectively modified onto the surface of CuInS 2 /3DNH and Bi 3+ /B-TiO 2 /rGO to construct a PEC aptasensor for the sensitive detection of ENR and CIP. Under optimal conditions, the proposed aptasensor exhibited wide linear ranges of ENR (0.01-10000 ng/mL) and CIP (0.01-1000 ng/mL), and relatively low detection limits of 3.3 pg/mL to ENR and CIP (S/N = 3). The aptasensor was successfully applied to the detection of ENR and CIP in milk samples., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Herein, an electrochemiluminescence (ECL) microRNA biosensor based on anti-fouling magnetic beads (MBs) and two signal amplification strategies was developed. The newly designed anti-fouling dendritic peptide was wrapped on the surfaces of MBs to make them resistant to nonspecific adsorption of biomolecules in complex biological samples so as to realize accurate and selective target recognition. One of the amplification strategies was achieved through nucleic acid cycle amplification based on the DNAzyme on the surfaces of MBs. Then, the output DNA generated by the nucleic acid cycle amplification program stimulated the hybrid chain reaction (HCR) process on the modified electrode surface to generate the other amplification of the ECL response. Titanium dioxide nanoneedles (TiO 2 NNs), as a co-reaction accelerator of the Ru(bpy) 2 (cpaphen) 2+ and tripropylamine (TPrA) system, were wrapped with the electrodeposited polyaniline (PANI) on the electrode surface to enhance the ECL intensity of Ru(bpy) 2 (cpaphen) 2+ . The conducting polymer PANI can not only immobilize the TiO 2 NNs but also improve the conductivity of the modified electrodes. The biosensor exhibited ultra-high sensitivity and excellent selectivity toward the detection of miRNA 21, with a detection limit of 0.13 fM. More importantly, with the anti-fouling MBs as a unique separation tool, this ECL biosensor was capable of assaying targets in complex biological media such as serum and cell lysate.

Sensitive detection of streptomycin (STR) has attracted increasing attention worldwide because of the relationship between food security and human health. In this paper, Bi 4 VO 8 Br/Ti 3 C 2 nanohybrids were obtained by one-pot solvent hydrothermal method. It was modified on ITO electrode, and STR aptamer was acted as the recognition element. With excellent photoelectrochemical (PEC) performance of Bi 4 VO 8 Br/Ti 3 C 2 nanohybrids, an "on-off-on" PEC aptasensor for STR detection was effectively developed. Compared with pure Bi 4 VO 8 Br, the photocurrent intensity of as-prepared Bi 4 VO 8 Br/Ti 3 C 2 nanohybrids was about 9 times higher, which ascribed to the highly conductive of Ti 3 C 2 , driving the photogenerated electrons transferred to the ITO electrode rapidly, so that the recombination of photogenerated electron and hole pairs was inhibited viably. Furthermore, the constructed "on-off-on" PEC aptasensor accomplished STR detection with high sensitivity, excellent specificity and distinguished repeatability in honey. The photocurrent increased with the increment of STR concentration with the linear range from1 nM to 1000 nM, and the detection limit of 0.3 nM (S/N = 3). Compared with the national standard method (SN/T 1925-2007), the as-constructed PEC sensor showed the consistent results., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A universal strategy for the construction of ratiometric antifouling electrochemical biosensors was developed based on multifunctional peptides and 2D nanomaterial MXene loaded with gold nanoparticles (AuNPs) and methylene blue (MB). The nanocomposite of MXene loaded with AuNPs and MB (MXene-Au-MB) exhibited excellent conductivity, where the AuNPs were able to capture biomolecules containing sulfhydryl terminus, and the MB molecules were used to generate electrochemical signal. The MXene-Au-MB was fixed on the electrode surface by Nafion, and the anchored peptide captured the electrochemical signal probe carboxyl-modified ferrocene (Fc) to construct an electrochemical biosensor. The multifunctional peptide containing the anchoring, antifouling, and recognizing sequences endowed the sensing surface not only the assaying function but also the capability to resist nonspecific adsorption from complex samples. In the biosensing system, with the increase in the target concentration, the electrochemical signal of MB remained constant, whereas the electrochemical signal of Fc gradually decreased, and the ratiometric detection strategy greatly improved the accuracy of the biosensor. In the presence of a model target prostate-specific antigen (PSA), the recognizing sequence was recognized and cleaved, and the ratiometric signal of Fc and MB indicated the concentration of PSA accurately and sensitively, with a detection range from 5 pg/mL to 10 ng/mL and a limit of detection of 0.83 pg/mL. Electrochemical biosensors based on the MXene-Au-MB and multifunctional peptides possessed high selectivity, accuracy, and sensitivity even in real complex biological samples because of the excellent antifouling ability of the peptide. More importantly, the assaying of other targets can be easily realized with a similar biosensing strategy by changing the recognition sequence of the multifunctional peptide, and the detection of thrombin (TB) has also been achieved in this work.

Biofouling caused by the accumulation of biomolecules on sensing surfaces is one of the major problems and challenges to realize the practical application of electrochemical biosensors, and an effective way to counter this problem is the construction of antifouling biosensors. Herein, an antifouling electrochemical biosensor was constructed based on electropolymerized polyaniline (PANI) nanowires and newly designed peptides for the detection of the COVID-19 N-gene. The inverted Y-shaped peptides were designed with excellent antifouling properties and two anchoring branches, and their antifouling performances against proteins and complex biological media were investigated using different approaches. Based on the biotin-streptavidin affinity system, biotin-labeled probes specific to the N-gene (nucleocapsid phosphoprotein) of COVID-19 were immobilized onto the peptide-coated PANI nanowires, forming a highly sensitive and antifouling electrochemical sensing interface for the detection of COVID-19 nucleic acid. The antifouling genosensor demonstrated a wide linear range (10 -14 to 10 -9 M) and an exceptional low detection limit (3.5 fM). The remarkable performance of the genosensor derives from the high peak current of PANI, which is chosen as the sensing signal, and the extraordinary antifouling properties of designed peptides, which guarantee accurate detection in complex systems. These crucial features represent essential elements for future rapid and decentralized clinical testing.

Sensitive detection of oxytetracycline (OTC) has attracted increasing attention worldwide due to the relationship between food safety and human health problems. In this work, a visible-light-driven photoelectrochemical (PEC) OTC aptasensor was constructed using Bi 4 VO 8 Cl/nitrogen-doped graphene quantum dots (Bi 4 VO 8 Cl/N-GQDs) nanohybrids as photoactive material and OTC aptamer as identification element. Owing to the well matched heterojunction of Bi 4 VO 8 Cl and nitrogen-doped graphene quantum dots (N-GQDs), the photogenerated electron-hole pairs could be separated effectively, so that the photocurrent intensity of as-prepared Bi 4 VO 8 Cl/N-GQDs nanohybrids was about 7 times higher than pure Bi 4 VO 8 Cl and had higher stability. The constructed "signal-off" PEC aptasensor realized OTC detection in tomato samples with excellent sensitivity, specificity and repeatability. The photocurrent decreased with the increase of OTC concentration in a range from 0.1 nM to 150 nM, and the detection limit was 0.03 nM (S/N = 3). The national standard method was used to compare with our method and the results were consistent., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this paper, an effective and accurate ratiometric electrochemiluminescence (ECL) system based on Au-luminol and CdS quantum dots (CdS QDs) as signal probes was constructed for detecting carcinoembryonic antigen (CEA). Polyaniline (PANI) and gold nanoparticles (AuNPs) strongly enhanced the electronic transfer efficiency and the specific area of the modified sensing surface, and improved the detection sensitivity. CdS QDs functionalized DNA strands functioned as cathode ECL emitters, and the aptamer of CEA modified with Au-luminol and quencher cyanine dye (Cy5) fluorophore functioned as anode ECL emitters. After the DNA capture probe combined with CEA aptamer, the negative potential ECL response of the CdS QDs was quenched because of electrochemiluminescence resonance energy transfer (ERET) between the Cy5 fluorophore and CdS QDs. However, the positive potential ECL response of Au-luminol can still be detected. The negative potential ECL response of CdS QDs was recovered, and the positive potential ECL response of Au-luminol decreased after CEA combined with its aptamer to take Cy5 and Au-luminol off the sensing interface. Additionally, the peptide provided effective anti-fouling performance in the detection of complex samples. The ratiometric ECL sensor with anti-fouling ability can sensitively determine the concentration of CEA in human serum., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Developing photoactive materials with wide spectral response is critical to improve the sensitivity of PEC biosensors. Herein, a sensitive photoelectrochemical (PEC) aptasensor was fabricated based on Bi surface plasmon resonance (SPR)-promoted BiVO 4 /g-C 3 N 4 (Bi/BiVO 4 /g-C 3 N 4 ) as photoactive material for the detection of oxytetracycline (OTC). Ternary Z-scheme Bi/BiVO 4 /g-C 3 N 4 heterojunction exhibited widest spectral response and best PEC activity compared to g-C 3 N 4 , BiVO 4 , Bi/BiVO 4 , and BiVO 4 /g-C 3 N 4 . The wide spectral response and high PEC activity could be attributed to three reasons: Firstly, the SPR effect of Bi could greatly increase light harvesting; Secondly, Bi served as an electron conduction bridge between BiVO 4 and g-C 3 N 4 to form Z-scheme structure, significantly accelerating the separation of photogenerated carriers; Thirdly, the synergism of Z-scheme heterojunction and the SPR effect of Bi efficiently boosted the photoelectric response. Based on the above sensitization strategies, the proposed PEC aptasensor for OTC determination showed a wide linear range of 0.01-1000 nM and a low detection limit (S/N = 3) of 3.3 × 10 -3  nM. Moreover, the high stability, satisfactory repeatability and favorable practicability of the fabricated PEC aptasensor revealed the potential applications for accurate monitoring of antibiotics in environmental media., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The modular nature of metal-organic frameworks (MOFs) permits their tunable structure and function for target application, such as in biomedicine. Herein, a green-emission Zr(IV)-MOF (BUT-88) was constructed from a customized luminescent carbazolyl ligand. BUT-88 represents the first bcu-type MOF with both organic linker and metal node in eight connections and shows medium-sized pores, rich accessible linking sites, and good water stability and biocompatibility. In virtue of these merits, BUT-88 was then fabricated into a MOF-based fluorescent nanoprobe, drDNA-BUT-88. Using it, the live-cell imaging of dual tumor biomarkers was achieved for the first time upon a MOF-based probe, offering enhanced detection precision in early cancer diagnosis. Particularly, the probe showed efficient ratiometric fluorescent sensing toward the cytoplasmic biomarker microRNA-21, further improving the detection accuracy at the cellular level. In this work, the elaborate combination of MOF engineering and the fluorescent detection technique has contributed a facile biosensing platform, unlocking more possibilities of MOF chemistry.

Self-powered sensor is considered as a promising, rapid, portable and miniaturized detection device that can work without external power input. In this work, a novel dual-photoelectrode self-powered aptasensor for digoxin detection was designed on the basis of a photofuel cell (PFC) composed of a black TiO 2 (B-TiO 2 ) photoanode and a CuBr photocathode in a single-chamber cell. The sensing platform avoided the use of membrane, free mediator, bioactive components and costly metal Pt electrodes. The large inherent bias between the Fermi energy level of B-TiO 2 and that of CuBr improved the electricity output of PFC that the open circuit potential (OCP) and the maximum power density (P max ) reached 0.58 V and 6.78 μW cm -2 respectively. Based on the excellent output of PFC, digoxin aptamer was immobilized on photoanode as the recognition element to capture digoxin molecules, which realized the high sensitive and selective detection of digoxin. The self-powered aptasensor displayed a broad linear in the range from 10 -12  M to 10 -5  M with a detection limit (3 S/N) of 0.33 pM. This work paved a luciferous way for further rapid, portable, miniaturized and on-site self-powered sensors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Nonspecific adsorption is of great concern for electrochemical biosensors performing in complex biological media, and various antifouling materials have been introduced into the sensing interfaces to improve the antifouling capability of different biosensors. However, for most of the biosensors with antifouling materials and sensing probes coexisting in the sensing interfaces, either the antifouling materials will impair the sensing performances or the sensing probes will affect the antifouling ability. Herein, a facile and efficient antifouling biosensor was developed based on a newly designed three-in-one peptide with anchoring, antifouling, and recognizing capabilities. One end of the designed peptide is a unique anchoring part that is rich in amine groups, and this part can be anchored to the poly(3,4-ethylenedioxythiophene) (PEDOT)-citrate film electrodeposited on a glassy carbon electrode. The other end of the peptide is a recognizing part that can specifically bind to the aminopeptidase N (APN) and human hepatocellular carcinoma cells (HepG2 cells). Meanwhile, the middle part of the peptide, together with the anchoring part, was designed to be antifouling. With this designed multifunctional peptide, highly sensitive and low-fouling biosensors capable of assaying target APN and HepG2 cells in complex biological media can be easily prepared, with detection limits of 0.4 ng·mL -1 and 20 cells·mL -1 , respectively. This antifouling biosensor is feasible for practical target detection in real complex samples, and it is highly expected that this peptide designing strategy may be extended to the development of various antifouling biosensors.

Developing a simple, rapid detection method for the analysis of edifenphos (EDI) is crucial due to its residue is harmful to acetylcholinesterase on the human cellular system, and cause a lot of complications. Herein, we synthesized visible light-responsive MoS 2 nanosheets decorated with Zinc phthalocyanine (ZnPc) nanoparticles (ZnPc/n-MoS 2 ). Due to the sensitization of ZnPc nanoparticles, the resulting ZnPc/n-MoS 2 exhibited narrower energy bandgap and efficient charge transfer. Especially, the carrier lifetime of ZnPc/n-MoS 2 is 2 more times longer than n-MoS 2 , and the photocurrent intensity of ZnPc/n-MoS 2 is 24 times of n-MoS 2 and 22 times of ZnPc nanoparticles under visible light irradiation. Further, a visible light-responsive ultrasensitive photoelectrochemical (PEC) aptasensor for selectivity recognition of EDI was triumphantly established by using EDI aptamer as a biorecognition element, which exhibited a wide linear ranking from 5 ng L -1 to 10 μg L -1 (R 2  = 0.996) and a low detection limit of 1.667 ng L -1 (S/N = 3). The splendid performance of the ZnPc/n-MoS 2 nanosheet ultrasensitive sensing platform can be applied to detect the concentration of EDI in food, biomedical and environmental analysis., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Sensitive and selective detection of target analytes in complex biological samples is currently a major challenge. Herein we constructed a dual-mode antifouling electrochemical sensing platform for the detection of prostate-specific antigen (PSA) based on two kinds of antifouling peptides functionalized with a graphene oxide-Fe 3 O 4 -thionine (GO-Fe 3 O 4 -Thi) probe and internal reference ferrocene (Fc), respectively. The longer peptide (Pep1) modified with the GO-Fe 3 O 4 -Thi probe was designed to contain a peptide sequence (HSSKLQK) capable of being recognized and cut by PSA. The GO-Fe 3 O 4 -Thi probe functions not only as a peroxidase mimick (GO-Fe 3 O 4 ) but also works as an electrochemical probe due to the presence of thionine (Thi). The concentration of PSA can be measured through both the increase of differential pulse voltammetry (DPV) signal change of Thi and the decrease of chronoamperometry (CA) signal of the reduction of H 2 O 2 electrocatalyzed by GO-Fe 3 O 4 . The shorter peptide (Pep2) was tagged with Fc, whose DPV signal remained constant and was independent of the presence of PSA, and it was used as an internal reference to ensure the reliability and accuracy of the measurement. The dual-mode PSA sensor exhibits a wide linear range from 5 pg/mL to 10 ng/mL, with low detection limits of 0.76 and 0.42 pg/mL through DPV and CA modes, respectively. More importantly, owing to the antifouling capability of the designed peptides, the biosensor performances remained operable even in human serum, indicating feasibility of the electrochemical biosensor for practical PSA quantification in complex samples.

Herein, we synthesized a kind of conductive supramolecular polymer hydrogel (CSPH) based on polyaniline (PANI) which can not only improve the conductivity but also promote antifouling performance of the aptasensor for the specific recruitment of thrombin (TB) from complex samples. With the electrochemical copolymerization of aniline (AN) and 3-aminophenylboronic acid (ABA) on glassy carbon electrode (GCE), the electrode was then inserted into the polyvinyl alcohol (PVA) solution to obtain robust CSPH through boric acid groups incorporated onto PANI to cause gelation of PVA solution, owing to the hydrophilicity of CSPH and nearly electrical neutrality, the modified electrode is antifouling without integration of other antifouling materials. A sandwich-type electrochemical aptasensor was constructed on the CSPH based electrode interfaces. Thrombin aptamer 1 (TBA1) were modified on the CSPH through amide bond, and thrombin aptamer 2 modified magnetic nanoparticles (MNP-TBA2) are used as signal amplification probes, the aptasensor has good sensitivity with a linear range from 1 pmol/L to 10 nmol/L and has a detection limit down to 0.64 pmol/L. The strategy of utilizing eletropolymerization of CSPH films to undergo highly selective thrombin recognition is, of course, readily extended to a broad range of targets in the real samples, and the recovery was ranging from 95.2% to 106.3% and RSDs varying from 2.3% to 4.5%., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this work, an antifouling electrochemiluminescent (ECL) ratiometric biosensor is designed for the accurate, selective and sensitive detection of DNA methyltransferase (MTase) activity based on a dual-signaling strategy. Briefly, an ITO electrode is used to construct the anti-fouling interfaces with the modification of polyaniline (PANI), AuNPs and peptide. Hairpin DNA molecules containing the symmetric sequence of 5'-CATC-3' are attached onto the modified ITO electrode and the ds-DNA can be cut off in the presence of Dam MTase and DpnI. The residual DNA and two hairpin DNA could lead to the extension of ds-DNA due to the Hybridization Chain Reaction (HCR). ECL signal is amplified significantly with the insertion of PTC-NH 2 molecules into the dsDNA grooves. The ECL PTC-NH2 /ECL Au@luminol is found in a logarithmic linear relation with the concentration of Dam MTase. Moreover, owing to the presence of antifouling peptide on the sensing interface, the ECL biosensor was capable of sensing MTase activity in complex biological media, such as FBS samples and human serum with significantly reduced nonspecific adsorption effect. Assaying Dam MTase in complex sample mixture containing 5% calf serum and 5% human serum further proved the feasibility of this ECL biosensor for early clinical diagnosis., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Oxygen defect-engineered is an important strategy to improve the photoelectric activity of materials. Herein, a facile one-pot solvothermal method was utilized to synthesize visible light-responsive photoactive Bi 2 MoO 6 nanoparticles anchored boron and nitrogen co-doped graphene (BNG) nanosheets nanocomposites with oxygen vacancy. The incorporation of BNG nanosheets increased the oxygen vacancies amounts on Bi 2 MoO 6 remarkably, and the presences of oxygen vacancies can be beneficial to broaden the absorption range. The absorption edge of Bi 2 MoO 6 /BNG was widened from 500 nm to 550 nm compared to Bi 2 MoO 6 , and the charge transfer was accelerated to improve the photoactive of Bi 2 MoO 6 /BNG. Under visible light illumination, the photoelectrochemical (PEC) response of the as-prepared Bi 2 MoO 6 /BNG was 11.6-fold, 6.7-fold, 3.1-fold and 2.4-fold higher than that of pristine Bi 2 MoO 6 , Bi 2 MoO 6 /graphene, Bi 2 MoO 6 /nitrogen doped graphene and Bi 2 MoO 6 /boron doped graphene. Using Bi 2 MoO 6 /BNG nanocomposites with the superior PEC performance as photoactive materials in combination with specifically recognized lincomycin (LIN) aptamer, a highly efficient PEC aptasensor was successfully constructed for sensitive analysis of LIN. Under optimal conditions, the proposed PEC aptasensor exhibited excellent analytical performance for LIN with a wide linear response of 1 × 10 -11 to 1 × 10 -6  mol L -1 along with a low detection limit of 3.7 × 10 -12  mol L -1 (defined as S/N = 3). The as-prepared Bi 2 MoO 6 /BNG nanocomposites exhibit excellent visible light response and PEC performance, indicating its potential applications in PEC biosensor., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this study, an ultrasensitive biosensor based on a novel electrochemiluminescence nanosurface energy transfer (ECL-NSET) system was developed for procalcitonin (PCT) detection. N-(Aminobutyl)- N-(ethylisoluminol) (ABEI) as ECL donor was externally cross-linked with ferritin (ABEI-Ft), whose ECL emission was boosted by a ferritin nanocore in the presence of hydrogen peroxide. Then single gold nanoparticles (Au NPs) as ECL acceptor were in situ reduced on the ABEI-Ft surface to fabricate a donor-acceptor nanostructure (ABEI-Ft@Au). ECL quenching that occurred in ABEI-Ft@Au correlates well with the NSET theory rather than Förster resonance energy transfer (FRET). To improve sensitivity of the biosensor, HWRGWVC heptapeptide (HWR) was utilized to capture the antibody Fc portion via specific interaction to realize site-oriented immobilization. After connecting with ABEI-Ft@Au via Au-S bonding, HWR improved the incubation efficiency of the antibody with a better maintained biological activity. Under optimal conditions, the proposed biosensor provided a quantitative readout to PCT concentration in the range of 100 fg/mL to 50 ng/mL with a detection limit of 41 fg/mL. With favorable specificity, stability, and reproducibility, this highly efficient ECL-NSET system will inspire more interest in nanometal-based ECL quenching mechanism studies and development of new methods for site-oriented antibody immobilization to improve sensitivity.

In this work, by using amorphous bimetallic sulfides of CoSnS x Pd as signal amplifier and magnetic material of Fe 3 O 4 @PPyAu as the substrate, we fabricated an electrochemical immunoassay for Nterminal prohormone of brain natriuretic peptide (NTpro BNP). CoSnS x was used as the signal amplifier of the immunosensor for the first time, which was synthesized by fast stoichiometric co-precipitation method. The binary sulfide was identified as an amorphous structure and performed apparent electrochemical behavior. The excellent performance of signal marker was induced by the synergistic effect between SnS 2 and cobalt, as well as the loaded Pd nanoparticles (NPs). Both CoSnS x and Pd NPs presented excellent electrocatalytic activity toward H 2 O 2 oxidation. Moreover, the magnetic nanocomposite of Fe 3 O 4 @PPyAu was firmly immobilized on the magnetic glassy carbon electrode (MGCE) by the magnetic force. The magnetic substrate not only performed good electron conductivity, but also improved the stability of the fabricated electrochemical immunosensor. The developed immunosensor for the NTpro BNP detection exhibited a wide linear response (0.1 pg/mL to 50 ng/mL), and low detection limit of 31.5 fg/mL. In addition, the immunosensor held an excellent analysis capability and broad fascinating application for the detection of other biomarkers in medical diagnosis and treatment., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Based on target-triggered dynamic hairpin assembly (DHA) in both unidirectional and bilateral growth manners DNA nanobrushes are constructed, which realize sensitive and selective detection of short miRNA (miR-21) and long DNA (BRCA1), respectively. Moreover, the unidirectional DHA strategy is readily applied to in situ imaging of miR-21 in different live cells.

A sensitive and reliable bimodal electrochemiluminescent (ECL) system based on CdTe quantum dots (QDs) and luminol as double luminophores is constructed. CdTe QDs tagged with the aptamer (CdTe-Apt 2) of cancer cells are used as the detection signals, while luminol molecules are used as internal standards. The electrodeposited polyaniline-based conducting polymer hydrogel (CPH) on the electrode surfaces improves the biocompatibility and conductivity of the sensing interfaces effectively. Furthermore, electron transfer is probably much easier when luminol and coreactant potassium persulfate (K 2 S 2 O 8 ) are immobilized in the CPH in comparison to that in solution. Cancer cells are captured to the electrode surface by another aptamer linked to the Au nanoparticles immobilized in the CPH through Au-S bonds. In the developed bimodal ECL system, an internal standard method is used to quantify cancer cells by comparing the differences in sensitivity of the double-peak ECL signals with that of target analytes. The internal standard method of ECL strategy can provide very accurate detection results in a complex environment because interferences in the system can be eliminated through the self-calibration of two emission spectra. A linear relation is found on the basis of a plot of the ΔECL CdTe /ΔECL luminol against the concentration of cancer cells within 100-6500 cells mL -1 under optimized conditions. The developed ratiometric ECL cytosensor with internal standard can significantly improve the accuracy and reliability of cell assays in complex biological media, demonstrating promising applications in healthcare monitoring and clinical diagnostics.

As a conventional amplification technique, polymerase chain reaction (PCR) has been widely applied to detect a variety of analytes with exponential amplification efficiency. However, the requirement of thermocycling procedures largely limits the application of PCR-based methods. Alternatively, several isothermal amplification techniques have been developed since the early 1990s. In particular, according to the reaction kinetics, isothermal exponential amplification techniques possess higher amplification efficiency and detection sensitivity. The isothermal exponential amplification techniques can be mainly divided into two categories: enzyme-based isothermal exponential amplification and enzyme-free isothermal exponential amplification. Considering the advantages of high sensitivity and selectivity, high signal-to-noise ratio, low cost and rapid response time, exponential amplification electrochemical biosensors have attracted considerable attention. In this review, we introduce the basic principles of isothermal exponential amplification techniques and summarize their applications in electrochemical biosensors during the past five years. We also highlighted the present challenges and further perspectives of isothermal exponential amplification-based electrochemical biosensors., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Based on the protective performance of polydopamine nanospheres (PDANSs) for DNA against nuclease digestion and the specific recognition characteristic of aptamer, we have developed an enzymatic recycling signal amplification method for highly sensitive and selective detection of adenosine triphosphate (ATP). Fluorescence measurements were carried out to verify the DNA polymerase and exonuclease III (Exo III) assisted target recycling process and fluorescence signal amplification. In the absence of the ATP, initially, the signal DNA-PDANSs complex was in the "off" state due to the efficient fluorescence quenching of 6-carboxyfluorescein (FAM) adjacent to the surface of PDANSs. Due to the binding of the aptamer by ATP, it trigger DNA polymerase and Exo III assisted target recycling process by the product of release, the complex would change into the "on" state as a result of the dissociation of the FAM from the surface of PDANSs, thus providing greatly enhanced fluorescence emission intensity. The method allows quantitative detection of ATP in the range of 20-600nM with a detection limit of 8.32nM. This biosensor requires no complex operations, and is a new high efficiency method for ATP detection., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Based on the extension reaction of a telomerase substrate (TS) primer in the presence of the telomerase, strand-displacement process to perform more stable longer duplex chain, and stepwise hydrolysis of mononucleotides from the blunt or the recessed 3'-hydroxyl termini of duplex DNA in the presence of Exonuclease III (Exo III), an amplified fluorescence detection of telomerase activity in the cancer cells was described in this manuscript. A fluorescence probe DNA, a quencher DNA, and a TS primer were mixed to construct a three-chain DNA structure and a two-chain DNA structure because the amount of the TS primer was less than the other two DNA. In the presence of the telomerase, the quencher DNA was replaced from the probe DNA and the telomerase activity could be determined with the fluorescence enhancement. The telomerase activity in HeLa extracts equivalent to 6-2000 cells was detected by this method. Moreover, the strategy was further proved by using telomerase extracted from Romas cells. With the multiple rounds of isothermal strand displacement and the hydrolysis process, constituted consecutive of signal amplification for the novel detection paradigm that allowed measuring of telomerase activity in crude cancer cell extracts confirmed the reliability and practicality of the protocol, which reveal this platform holds great promise in the biochemical assay for the telomerase activity in early diagnosis for cancers., (Copyright © 2016 Elsevier B.V. All rights reserved.)

An electrochemical biosensor based on rolling circle amplification (RCA) and nanoparticle aggregates for highly sensitive identification of DNA and cancer cells were established in this work. First, a "sandwich-type" DNA complexes containing target DNA was constructed on the surface of the magnetic beads. Second, one part of the primer in the "sandwich-type" DNA complexes induced the RCA in the system. Then the long RCA products were digested to construct another "sandwich-type" DNA complex for the electrochemical detection. Differential pulse voltammetry (DPV) peaks with high signal intensity were obtained, and the signal intensities were found to be dependent on the amount of Fc, which is related to the concentration of target DNA. Under the optimum conditions, the electrochemical signal intensity was increased with the increase of the concentration of target DNA. A detection limit of 2.8×10⁻¹⁸ M of target DNA was achieved. Combined with aptamers technology, the proposed signal amplification strategy was also used for the identification of cancer cells with the detection limit of 100 Ramos cells mL⁻¹., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A PCR (polymerase chain reaction)-free electrochemiluminescence (ECL) strategy based on aptamers and ECL nanoprobes was developed for rapid collection and detection of Ramos cells. The ECL nanoprobes consisted of gold nanoparticles (AuNPs), linker DNA and tris-(2,2'-bipyridyl) ruthenium (TBR)-labeled signal DNA. The linker DNA and signal DNA were modified on the surface of the AuNPs through AuS bonds. The linker DNA can hybridize partly with the aptamers loaded on the magnetic beads to construct the magnetic biocomplex. In the presence of the cancer cells, the aptamers conjugated with the cancer cells with higher affinity. The ECL nanoprobe released from the biocomplex and subsequently hybridized with the capture DNA modified on the Au electrode. The ECL intensity of the TBR loaded on the nanoprobes directly reflected the amount of the cancer cells. With the use of the developed ECL probe, a limit of detection as low as 50 Ramos cells per mL could be achieved. The proposed methods based on ECL should have wide applications in the diagnosis of cancers due to their high sensitivity, simplicity and low cost., (Copyright © 2012 Elsevier B.V. All rights reserved.)

An electrochemical cytosensor was designed based on the specific recognition of mannosyl on a cell surface to concanavalin A (ConA) and the signal amplification of gold nanoparticles (NPs). By sandwiching a cancer cell between a gold electrode modified with ConA and the gold NPs with ConA and 6-ferrocenylhexanethiol (Fc), the electrochemical cytosensor was established. The cell number and the amount of cell surface mannose moieties were quantified by cyclic voltammetry (CV) analysis of the Fc loaded on the surface of the gold NPs. Since a single gold NP could be loaded with hundreds of Fc, a significant amplification for the detection of target cell was obtained. By using K562 leukemic cells (K562 cells) as a model, the electrochemical response was proportional to the cell concentration in the range from 1.0×10(2) to 1.0×10(7) cells mL(-1), showing very high sensitivity. The signal amplification could be further used to evaluate the cell surface mannose moieties, and the amount of mannose moieties on a single living K562 cell was detected to correspond to 4.7×10(9) molecules of free mannose. This strategy presents a promising platform in a highly sensitive cytosensor and convenient estimation of cell surface carbohydrate., (Copyright © 2011 Elsevier Inc. All rights reserved.)

A novel electrochemical assay based on the aptamer and the signal of amplification of nanoparticles (NPs) was constructed for the determination of thrombin. Aptamers immobilized on the electrode and Au NPs could be assembled with the target protein to form a sandwich structure in the presence of the latter. Differential pulse voltammetry (DPV) was employed to detect the CdS NPs loaded on the surface of the Au NPs through the linker DNA, which was related to the concentration of the target protein. The assay took advantage of the amplification ability of Au nanoparticles carrying multiplex CdS NPs and the specific affinity of aptamers. Thrombin was detected in this assay in the linear range of 1.0x10(-15) to 1.0x10(-11) M with the detection limit of 5.5x10(-16) M of target protein. In addition, the assay could be used to detection thrombin in real samples with high sensitivity and good selectivity., (Copyright 2009 Elsevier B.V. All rights reserved.)

We describe herein the combination of electrochemical immunoassay using nanoporous gold (NPG) electrode with horseradish peroxidase (HRP) labeled secondary antibody-gold nanoparticles (AuNPs) bioconjugates for highly sensitive detection of protein in serum. The electroactive product of o-phenylenediamine (OPD) oxidized with H(2)O(2) catalyzed by HRP was reduced in the Britton-Robinson (BR) buffer and the peak current of which was used to determine the concentration of antigen (Ag) in the analyte. The active surface area of NPG electrode was larger than that of a bare flat one. The presence of AuNPs enhanced the immobilized amount of HRP labeled antibody (Ab), which improved the sensitivity of the immunoassay when used as the secondary antibodies. As a result of these two combined effects, the sensitivity of the immunoassay for the determination of target protein was increased significantly. Using hepatitis B surface antigen (HBsAg) as a model, we demonstrate a dose response in the range of 0.01-1.0ng/mL with a detection limit of 2.3pg/mL. Analytical results of several human serum samples obtained using the developing technique are in satisfactory agreement with those given by enzyme-linked immune-absorbent assays (ELISA). In addition, the technique was about 100 times more sensitive in the detection of HBsAg than ELISA. All these demonstrated the feasibility of the present immunoassay method for clinical diagnosis.

Based on the electrochemical detection of cadmium ions dissolved from CdS nanoparticles (NPs), a novel and sensitive assay for the sequence-specific DNA detection has been developed by using bio-bar code techniques. The "sandwich-type" DNA complexes were fabricated with the thiol-functionalized capture DNA firstly immobilized on the modified electrode (nanoAu-GCE) and hybridized with one end of target DNA, the other end of which was recognized with signal DNA labeled on the surface of Au NP. To amplify the detection signals, the Au NP was also modified with CdS NPs by an amidization reaction between bio-bar code binding DNA on the surface of Au NPs and mercaptoacetic acid on the surface of CdS NPs. The hybridization events were monitored by the electrochemical detection after the cadmium ions were dissolved from the hybrids. Under optimum conditions, the peak current value was increased with the increase of the concentration of target DNA in the range of 1.0x10(-14) to 1.0x10(-13) M. A detection limit of 4.2x10(-15) M of target DNA was achieved. The ASV currents of two-base mismatched sequences and non-complementary sequences were also detected. The experiments indicated that two-base mismatched sequences showed weaker peak current and non-complementary sequences gave no response at all.

A novel and effective electrochemical immunosensor for the rapid determination of alpha-fetoprotein (AFP) based on carbon paste electrode (CPE) consisting of room temperature ionic liquid (RTIL) N-butylpyridinium hexafluorophosphate (BPPF(6)) and graphite. The surface of the CPE was modified with gold nanoparticles for the immobilization of the alpha-fetoprotein antibody (anti-AFP). By sandwiching the antigen between anti-AFP on the CPE modified with gold nanoparticles and the secondary antibody, polyclonal anti-human-AFP labeled with horseradish peroxidase (HRP-labeled anti-AFP), the immunoassay was established. The concentration of AFP was determined based on differential pulse voltammetry (DPV) signal, which was generated in the reaction between O-aminophenol (OAP) and H(2)O(2) catalyzed by HRP labeled on the sandwich immunosensor. AFP concentration could be measured in a linear range of 0.50-80.00 ng mL(-1) with a detection limit of 0.25 ng mL(-1). The immunosensor exhibited high sensitivity and good stability, and would be valuable for clinical assay of AFP.

Composite material based on room temperature ionic liquid (RTIL) N-butylpyridinium hexafluorophosphate (BPPF(6)), sodium alginate (SA), and graphite was used to construct a novel horseradish peroxidase (HRP) biosensor for the determination of H(2)O(2). The morphology of the as-prepared biosensor was characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the process of the performance of the biosensor. Parameters affecting the performance of the biosensor, including the concentrations of o-aminophenol (OAP) and HRP and the pH value of substrate solution, were optimized. Under the optimized experimental conditions, H(2)O(2) could be detected in a linear calibration range of 1.0 to 6.0 microM with a correlation coefficient of 0.9847 (n=7) and a detection limit of 0.5 microM at a signal/noise ratio of 3. The prepared biosensor not only had economic and disposable property but also showed good detection precision, bioactivity, storage stability, and reproducibility.

A label-free biosensor for the detection of oligonucleotides related to hepatitis B virus sequence via the interactions of DNA with redox-active complex, 2,9-dimethyl-1,10-phenantroline cobalt [Co(dmp)(H2O)(NO3)2] is described. The study was carried out by the hybridization of 21-mer probe DNA modified on glassy carbon electrode (GCE) with target DNA, and [Co(dmp)(H2O)(NO3)2] whose sizes are comparable to those of the small groove of native double-helix DNA was used as an electrochemical indicator. Electrochemical detection was performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) over the potential range where the [Co(dmp)(H2O)(NO3)2] was active. Under the optimum conditions, the electrical signal had a linear relationship with the concentration of target DNA ranging from 3.96 x 10(-7) to 1.32 x 10(-6) M, and the detection limit was 1.94 x 10(-8) M (S/N=3). The biosensor has good selectivity by detecting the three-base mismatch sequence ssDNA.