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β-Glucuronidase (β-GCU) is closely related to the occurrence of multiple diseases, and it has been applied as a biomarker and therapeutic target in clinical diagnosis. However, reliable methods with high selectivity and sensitivity for monitoring β-GCU are still lacked. Herein, we designed a novel fluorescent nanoprobe, rhodamine B encapsulated MOF-5 (RhB@MOF-5) for the first time, to detect β-GCU through the synergistic effect of inner filter effect (IFE) and static quenching effect (SQE) by employing 4-nitrophenyl-β-D-glucuronide (PNPG) as the substrate. After encapsulating into MOF-5, the fluorescence emission of RhB at 550 nm excited by 320 nm was greatly enhanced. The major overlap between the fluorescence excitation spectrum of RhB@MOF-5 (about 320 nm) and the ultraviolet absorption spectrum of PNPG (about 310 nm) lead to PNPG being a good IFE absorber in this sensing system. Under the optimized conditions, the excitation spectrum of the RhB@MOF-5 could be absorbed by PNPG, resulting in the dramatically decrease of fluorescence emission. After adding β-GCU into the system, the substrate of PNPG would be enzymatic hydrolyzed to p-nitrophenol (PNP) and glucose, then the IFE disappearance and the fluorescence recovered. The current sensing platform was interference-free and exhibited a broad linearity relationship for β-GCU range of 0.1–10 U L−1 (R2 = 0.9957) with a limit of detection as low as 0.03 U L−1, which was reduced by more than one orders compared with the reported methods. Moreover, the encapsulation of dyes using porous nanoparticles to achieve some tailor-made characteristics will enrich experimental design inspiration.

Here, a pH-responsive ZnO nanoprobe mediated DNAzyme signal amplification strategy was proposed for sensitive detection and live cell imaging of multiple microRNAs. The nanoprobe including ZnO nanoparticles (ZnO NPs) core as carrier and cofactor provider and polydopamine shell for adsorption the functional hairpin DNAs was designed. When nanoprobe entered the cell through endocytosis, the acidic environment of the cell could decompose the ZnO NPs core to release the functional hairpin DNAs and Zn2+. The Zn2+ could act as cofactor for the DNAzyme cleavage amplification reaction, avoiding additional cell delivery processes. The recognition hairpin DNAs (H1 and H3) recognized microRNA and exposed the DNAzyme. The DNAzyme cleaved cyclically the reporter hairpin DNAs (H2 and H4), producing enhanced fluorescent signal for miR-21 and miR-373 detection with the detection limit of 54 pM and 38 pM, respectively. Expression levels of miR-21 in Hela, HepG-2 and L02 cells were differentiated. Furthermore, simultaneous imaging of miR-21 and miR-373 in same living cells was achieved. These results indicated this strategy could have a potential application in microRNAs assays for the accurate diagnosis and therapy of cancer.

A label-free and turn-off fluorescence method for detecting cytochrome c (Cyt c) was developed using enhanced DNA-templated silver nanoclusters (DNA-AgNCs@tween 80) as a novel fluorescence-enhancing nanoprobe. Cyt c-induced electron transfer between Cyt c and DNA-AgNCs results in a significant fluorescence quenching effect of DNA-AgNCs. The coated tween 80 around DNA-AgNCs particles significantly causes fluorescence signal enhancement in the solution. Meanwhile, the efficiency of fluorescence quenching by Cyt c increases substantially by adding 0.1% tween 80 (final volume concentration) into the detection system. Based on these findings, a simple method with the detection limit of 0.8 nM was established for Cyt c based on tween 80 enhanced DNA-AgNCs. A good linear relationship between the fluorescent intensity and the concentration of Cyt c ranging from 0.8 nM to 20,000 nM (R2 = 0.9910) was obtained. Consequently, the method was applied to monitor the Cyt c variation in HCT-116 and BGC-823 tumor cell culture medium after being treated with doxorubicin (DOX)and two kinds of natural compounds (J5 and S6, extracted from plants Abacopteris Penangiana and Swertia punicea Hemsl, respectively). The results indicate that the level of Cyt c in cell culture medium decreases according to the presence of DOX, J5 and S6. The reliability of the result was further confirmed by using cell viability assay and flow cytometry for apoptosis analysis (FACS). From these data, it can be concluded that this groundbreaking nanoprobe with high sensitivity, great simplicity and good biocompatibility boosts a promising outlook for exploring the molecular mechanisms of apoptosis regulation and nature drugs screening.

Herein, we have developed an efficient approach for folate receptor (FR) over expressed cancer cell targeting and imaging through non-covalent conjugation between folic acid (FA) and a polyfluorene based amphiphilic, fluorescent polymer nanoprobes (CPF) by fluorescence “turn off” mechanism. The pH dependent supramolecular complexation/decomplexation tendency of CPF nanoprobes with FA provides the effective reversible fluorescence “turn off/turn on” of CPF fluorescence. The complete pH dependent complexation/decomplexation phenomena is characterized by photophysical and morphological characterization. The FESEM image study reveals the alteration of nanosphere structure of CPF to interconnected network after complexation with FA at pH 9 and consequently restoration of nanosphere morphology by decomplexation at pH 2. Again, the CPF nanoprobes exhibit 91% fluorescence quenching even in physiological pH 7.4 to reveal that the nanoprobes can be a suitable candidate for FA targeted turn-off fluorescent nanoprobes for FA pre-treated FR-positive cancer cells in vivo study. The fluorescence of CPF nanoprobes is significantly quenched in FA pre-treated FR-positive B16F10 cancer cell whereas it remains unchanged in FR-non overexpressed normal human corneal cell (HCE cells) even after FA pre-treatment. Furthermore, the present study can provide a dissimilar protocol to use a “turn off” fluorescent nanoprobe for FR-positive cancer cell imaging using free FA and fluorescent polymer nanoparticle rather than the conventional direct FA-fluorescent conjugated polymer complex.

MXenes as a new class of 2D materials have recently been widely applied in energy storage, electrocatalysis, sensors, adsorption, water purification, and so on, due to their tunable versatile properties. Herein, we demonstrate a simple, rapid and highly-sensitive sensing platform based on ultrathin two-dimensional MXene Ti3C2 nanosheets (Ti3C2 NSs) for selective analysis of Human papillomavirus (HPV), a major human pathogens and causative agents of cervical cancer. Ultrathin Ti3C2 NSs, obtained by exfoliating their layered HF-etched powder, exhibit high fluorescence quenching ability to dye-labeled single-stranded DNA (ssDNA) and different affinities for ssDNA and double-stranded DNA (dsDNA). Under the fluorescence quenching effect of Ti3C2 NSs, ssDNA probe (P) shows the minimal fluorescent emission. After the formation of duplex structure with its complementary target, ssDNA (T), the fluorescence intensity enhances evidently. Exonuclease III (Exo III) was used to improve the sensitivity by promoting more fluorescence enhancement. This magnified fluorescent sensor for HPV-18 detection shows a low detection limit of 100 pM and a high specificity. Furthermore, the developed DNA sensor can be employed to determine PCR amplified HPV-18 from cervical scrapes samples. It highlights ultrathin Ti3C2 NSs as a potential candidate for construction of fluorescence DNA biosensors with excellent performances.

Two-photon excitation (TPE) has excellent properties, such as lower tissue self-absorption and autofluorescence, reduced photodamage and photobleaching, and higher spatial resolution. Meanwhile, DNAzyme has significant signal amplification ability, and the gold nanoparticle (AuNP)-based spherical nucleic acid (SNA) has the properties of resistance to enzymatic degradation, enhanced nucleic acid binding and excellent cellular uptake. Taking advantage of their properties, in this work, we constructed a novel SNA-based TPE fluorescent DNAzyme probe for the selective and sensitive detection of target miRNA in living cells. Briefly, AuNPs were first functionalized with the substrate sequences hybridized to two split fragments of the 8–17 DNAzyme-contained sequence. Then, numerous two-photon absorption (TPA)-dye molecules of Ethyl-4-[3,6-Bis (1-methyl-4-vinylpyridium iodine)-9H-carbazol-9-yl)] (EBMVC) were inserted into the substrate/split-DNAzyme duplexes on the surface of the AuNP to form the TPE SNA nanoprobe in the “off” fluorescence emission state. When the target miRNA is bound, the conformation of the split DNAzymes will change resulting in the activation of their catalytic ability, thus leading to cleavage of the substrate sequences and the release of the TPA-dye molecules-inserted DNAzyme motif from the surface of the AuNP. Concurrently, the released target miRNA would autonomously hybridize with another split DNAzyme motif and activate further cleavage reactions. This would induce the gradual dissociation of the TPA-dye molecules-inserted DNAzyme motifs from the surface of the AuNP through the repeated target miRNA hybridization-activated cleavage reaction and thereby trigger the cascade TPE fluorescence emission, ultimately achieving the detection of the miRNA through amplification of the fluorescence signals. The assay was successfully validated with clean buffer conditions as well as with cells.

Histidine is one of the essential amino acids in the human body, and the variation of its concentration in vivo has shown it to align with some liver and kidney diseases. In this work, a series of novel poly(2-oxazoline) derivatives bearing chiral pyrrolidine–triazole moieties in the side chain were designed and synthesized to serve as chemical sensors for histidine. The results demonstrated that the homopolymer HPOx2 is capable of selectively binding optically active histidine through nitrogen/Cu2+ coordination to form complexes exhibiting induced circular dichroism (ICD) signals with signs related to the absolute configuration of the guest compound. Interestingly, the micelle-type nanoparticles assembled from the corresponding amphiphilic copolymer (CPOx2) gave a much stronger CD response, with an intensity five times that of its small molecule- or homopolymer counterparts. The proposed method, based on the chiroptical probe, allows for enantioselective detection of histidine in aqueous media, showing potential application in the field of biomedical assay and chiral drug synthesis.

Here, we fabricated a new amine compound as the co-reactant and incorporated an ECL sensor based on RuSi NPs/Nafion to improve the detection sensitivity of ECL system toward H2S by enhancing ECL intensity. The prepared sensor shows a good detection effect. In the work, water-oil microemulsion method was used to synthesize the Ru(bpy)32+-doped silica nanoparticles (RuSi NPs), and then mixed the RuSi NPs solution with Nafion (5 wt%) followed by modifying the mixture to the electrode. Upon treatment with H2S, the co-reactant NBD (7-nitro-1,2,3-benzoxadiazole) can release the piperazine intermediate, which can effectively improve the ECL signals of Ru(bpy)32+. This enhanced ECL assay for H2S detection have the following several merits: excellent sensitivity with the detection limit of 1.7 × 10−12mol/L, good selectivity over interfering species.

Highly reliable detection, imaging, and monitoring of reactive oxygen species (ROS) at subcellular organelles are critical for understanding the biological roles of ROS and learning the pathogenesis of some diseases. In this study, we presented an interference-free surface-enhanced Raman scattering (SERS)-active nanoprobe for the intracellular ROS detection. This nanoprobe was designed as an Au core-Ag shell nanoparticle (Au@Ag NPs) with a SERS reporter (4-mercaptobenzonitrile) resided in the inner of the core-shell. Intracellular ROS is able to etch the Ag shell and dramatically decreases the SERS intensity of the SERS reporters. It is worth mentioning that the Raman band of the reporter we used in this study locate in the cellular Raman-silent region (1800–2800 cm−1), which eliminates interference possibility from cellular molecules. The shell can also further protect the reporters from the interference of mediums. We detected ROS at subcellular organelle level, e.g. mitochondria, by modifying the surface of the nanoprobes with a mitochondria-targeting peptide. And for the first time, the SERS-based monitoring of ROS at mitochondria during the photothermal therapy process was validated and the profiles of the ROS distribution were disclosed by SERS mapping.

Quantum dots (QDs) as fluorescence probes have attracted increasing attention for their fluorescence imaging applications. In this work, we developed a novel strategy to create bifunctional silica-protected QD (BSQD) nanoparticles as nanoprobes for fluorescence imaging. The thiol-ene click reaction of monounsaturated fatty acid salts with mercapto silane as an efficient method for the synthesis of the bifurcated surface modifier was presented. BSQD nanoprobes were prepared by a facile one-pot method. The whole reaction process was carried out in an aqueous solution under relatively low temperature, which makes the synthesis environment eco-friendly and the products cost-effective. The synthesized BSQD nanoprobes have a structure consisting of hydrophilic and hydrophobic arms that afforded an amphiphilic feature to the silica-protected QD (SQD) nanoparticles. The separated solid BSQD nanoprobes could be well dispersed into aqueous solution once again, and the quantum yield of the BSQD nanoprobes was higher than that of the SQD naoprobes. BSQD nanoprobes exhibited high interfacial activity, strong photostability and good biocompatibility. BSQD nanoprobes were successfully applied for fluorescence imaging. The strategy for the construction of the functionalized SQD nanoparticles provides a promising approach for modifying the surface of materials containing QDs.

The emergence of novel lysosome-targetable and ratiometric fluorescent probes for visualizing intracellular hypochlorous acid (HClO) is useful for exploring HClO-associated diseases. However, the notorious aggregation-caused quenching (ACQ) effect universally observed in conventional organic small lysosomal HClO fluorescent probes could greatly limited their biological applications. In addition, the “alkalizing effect” of morpholine group severed as the lysosome guiding unit would also lead to the enhancement of lysosome pH and even cell apoptosis. To circumvent the above problems, we herein report on the fabrication of a simple yet efficient polymeric nanoparticles-based ratiometric fluorescence nanoprobe (PNRFN) for lysosomal HClO imaging in living cells. The unique nanostructure can not only effectively separate the HClO sensing unit (on the surface of nanoparticles) and aggregation induced emission (AIE)-based reference fluorogen (in the core of nanoparticles) to prevent severe ACQ phenomenon, but also possess high water solubility, well-resolved fluorescence signals, good biocompatibility and excellent photostability, etc. Significantly, thanks to the positive charge and good cell-membrane permeability of nanoparticles, the as-prepared PNRFN can selectively accumulate in lysosomes, and it can be further successfully used to tracking exogenous/endogenous HClO in lysosomes. We expect that such ratiometric nanoprobe with well-resolved emission spectra can be served as an excellent platform for targeting specific biomolecule populations at subcellular levels.

A surface-enhanced Raman scattering (SERS)-based lateral flow immunosensor was created to identify colistin in milk. The Raman reporter 5,5-dithiobis-2-nitrobenzoic acid (DTNB) was used to label gold nanoparticles, and then anti-colistin monoclonal antibody (mAb) was attached. The size of the gold nanoparticles in the SERS nanoprobe was optimized, and the amount of DTNB and mAb, the change in hydrodynamic size, zeta potential, and the surface plasmon resonance band were also monitored in the preparation process. The SERS nanoprobe was then applied to a lateral flow strip followed by Raman signal readout for the quantitative determination of colistin with high sensitivity. The limits of detection of this assay were 0.10 ng/mL for colistin in milk, which was far below the previously reported value that was obtained with the ELISA method and the maximum residue limit set by the European Union. The spiking experiment showed high accuracy for this SERS-based immunosensing assay, with a recovery of 88.1%–112.7% and satisfactory assay precision with a standard deviation below 15%. Furthermore, this assay also has the advantage of rapidity, with an assay time less than 20 min. Therefore, these results demonstrate that this SERS-based lateral flow immunosensor is promising for use in the rapid monitoring of colistin in milk.

Without any surfactant or organic solvent, a water-borne method incorporated a biphasic sol-gel process and a Pickering emulsion process was firstly applied to encapsulate lanthanide complexes. Compared with the free one, the achieved double protected lanthanide fluorescence colloidal hybrid particles with core@shells structure has a specific ClO− detection with high selectivity and sensitivity in contrast with other inorganic ions including Cu2+, Fe3+ and other strong acids. With strong oxidation characteristics, ClO− can gradually penetrate through silica shell, and quench the red fluorescence of lanthanide ions in the organosilica core. This core@shell colloidal nanoprobe exhibits an excellent sensing capacity for hypochlorite in real sample. This green environment friendly method could be easily extended to form functional hybrid particles with other types of reactive oils and nanoparticles for devising other specified fluorescent sensors.

Near-infrared (NIR) fluorescent sensors have been actively pursued due to organisms exhibiting little autofluorescence in near-infrared regions. Capable of emitting luminesence under 980 nm excitation, upconversion nanoparticles have shown promise as optical agents for in vivo bioimaging. Based on luminescence resonance energy transfer (LRET), a NIR luminescent Arg-nanoprobe was developed by the decoration of upconversion nanoparticles (UCNPs) (NaYF4:Yb,Er) with organic molecules. The as-developed nanoprobe could quantitatively detect concentrations within the range of 528–1250 μM, and had high sensitiviy (the limit of detection, LOD, being 15.6 μM) and good photostability. Because the probe could target lysosomes, intracellar detection of Arg behavior was demonstrated via upconversion luminescence (UCL) imaging.

Chemiluminescence (CL) of luminol is a well-established technology for in vitro biochemical analysis of hydrogen peroxide (H2O2). However, applications of chemiluminescence as a signal transduction trigger for fluorophore release still remain to be exploited. In this paper, we rationally design a chemiluminescence-triggered fluorophore release approach for imaging of H2O2 in vivo. The o-benzyl alcohol-decorated block poly(carbonate)s copolymer, viz. PMPC−ONA, was synthesized affording the final formation of the H2O2 responsive micelles, in which luminol, fluorophore, and hemin were wrapped forming L/H/S@PMPC−ONA nanoprobe. The presence of H2O2 diffuses into the nanoparticles and reacts with the hemin, generating high-energy reactive oxygen that could chemically excite the luminol triggering the chemiluminescence for cleaving nitrosobenzaldehyde recognition sites. The process could lead to destabilize the micelles and release the fluorescent indicator for imaging of H2O2. The concentration of H2O2 can be determined from 0.02 to 100 μM with a detection limit of 0.01 μM. The feasibility of L/H/S@PMPC−ONA is demonstrated for investigating fluorescence imaging of endogenous H2O2 in cells and mice. As far as we know, this is the first paradigm of rationally designed chemiluminescence as a signal transformation trigger for fluorophore release.

Cyanide anion is an inhibitor of the enzyme cytochrome c oxidase in the fourth complex of the electron transport chain, and usually found in the membrane of the mitochondria of eukaryotic cells, thus exploration of novel analytical methodology for sensitive and accurate detection of cyanide ion in cells is vital and urgent. Herein, we successfully prepared and surface-modified ZnGa2O4:Mn2+ PLNPs with excellent afterglow properties, small size and preferable dispersibility. Furthermore, we report a rational design and fabrication of a functional PL nanoprobe based on luminescence resonance energy transfer (LRET), which for the first time demonstrates detection of cyanide ion without external illumination. The nanoprobe is composed of two main moieties: PLNPs with excellent afterglow properties as energy donor; and DEHSPI, a chromophore with tunable light absorption, as both energy acceptor and CN− recognition element. PL can be effectively quenched by the chromophores assembled on the surface of PLNPs through a LRET process and subsequently recovered upon the addition of CN−. Importantly, the persistent afterglow nature highlights the merits of employing PLNPs as energy donor to eliminate the background noise under in situ excitation. Moreover, the nanoprobe exhibits excellent analytical properties and low cytotoxicity for bio-imaging of CN− in living cells.

Glutathione (GSH) is an important intracellular antioxidant. It is closely related to the homeostasis of the intracellular redox state which can be changed through deoxynivalenol (DON) exposure. More importantly, GSH deficiency can directly lead to apoptosis and cellular metabolic disorders mediated by intracellular redox homeostasis. Therefore, real-time monitoring of dynamic changes of GSH levels in living cells is urgently needed for the evaluation of intracellular oxidative stress. Herein, for the first time, an aptamer-based recognition composite nanoprobe (Apt-AuNCs-MoS2) was successfully constructed. The nanoprobe was employed for real-time and in situ imaging of DON-induced intracellular GSH changes and evaluation of oxidative stress status. The results indicated that the aptasensor revealed excellent specificity and high sensitivity to GSH in the solution system, and the limit of detection was as low as 35 nM. The results about DON-mediated oxidative stress indicated that the oxidative stress in living cells tends to be saturated with more than 20 ppm DON concentration. Thus, the strategy provides a novel aptasensor for the determination of GSH, offers a promising platform for fluorescence imaging of intracellular GSH in living cells, and further enriches in situ analysis of the in vitro toxicology.

Developing fluorescent probes to detect reactive oxygen species (ROS) is imperative to understanding the vital roles of ROS in various signaling and pathological processes. In this work, UiO-66-NH2 could be readily utilized as self-calibrating nanoprobe for selective detection and bioimaging of hypochlorite. Under the excitation of 400 nm, UiO-66-NH2 featured an emission at 432 nm and a new emission at 533 nm appeared after the addition of ClO-. Besides, the emission intensity of 533 nm increased with the incremental amount of ClO-. By using the ratio I533 nm/I432 nm as detection signal, UiO-66-NH2 could discriminate ClO- with high performance. The linear working range towards ClO- is 0.1–150 μM and the detection limit is 63.8 nM. In contrast to most other ratiometric sensors fabricated by physical entrapment methods, UiO-66-NH2 has the obvious advantage of effectively avoiding the worry of leakage of fluorophores from the nanomaterial matrix of sensors leading to erroneous measurements. Other amino-group functionalized MOF-based sensors such as MIL-53-NH2(Al) and MIL-101-NH2(Fe) exhibited similar fluorescence response toward ClO- as UiO-66-NH2. This work raises the possibility to develop highly specific and efficient probe for ClO- detection in vivo or in living cells and presents a new insight into ratiometric sensors.

Early and accurate diagnosis of pathogenic bacteria is essential to prevent further infection from spreading and multiplying. Herein, an aptamer (Apt) biosensor based on Fe3O4@Au nanocomposites (NCs) has been proposed for capture, surface-enhanced Raman scattering (SERS) detection, and photothermal therapy (PTT) of S. aureus. Fe3O4@Au NCs become SERS substrate and photothermal agent due to superior surface plasmon properties and photothermal ability, while the aptamer immobilized on surface of Fe3O4@Au NCs acts as a capture agent. The detection limit of optimized Fe3O4@Au-Apt aptasensor for S. aureus is 25 cfu/mL, and cell capture efficiency (CCE) is as high as 68%. Moreover, our Fe3O4@Au-Apt NCs have high photothermal conversion efficiency of 39.28%, which have been proven as an excellent photothermal agent. As verified by experiments, Fe3O4@Au-Apt aptasensor is not only a promising tool to detect and photothermally inactivated S. aureus in milk samples, but also exhibits negligible cytotoxicity and good biocompatibility. This work shows a promising multifunctional nano-platform, which has great potential in specific recognition, sensitive SERS detection and PTT of S. aureus.

Foodborne pathogens could result in serious health issues to public and thus some rapid analysis methods are urgent developed to monitor them. Herein, a dual-mode aptasensor based on electrochemical and colorimetric modes was constructed for the on-site detection of Vibrio parahaemolyticus (V.P) in shrimps as a model. A novel nanoprobe (PBA-Fc@Pt@MXenes) was developed to generate both electrochemical and colorimetric signals by modifying phenylboronic acid and ferrocene on Pt-MXenes nanocomposite. The nanoprobe exhibited both features of peroxidase mimic and specific recognition. Simultaneously, a V.P aptamer-functionalized electrode interface was fabricated to firstly specifically capture V.P, then conjugated with PBA-Fc@Pt@MXenes to form a sandwich complex. The complex could catalyze tetramethylbenzidine (TMB)-H2O2 to produce a visible signal, and generate electrochemical signal simultaneously. Under the optimal condition, the aptasensor could determine as low as 5 CFU mL−1 V.P by electrochemical mode and 30 CFU mL−1 V.P by colorimetric mode. These superior performances may be attributed to that the synergistic catalysis and conductive effects deriving from Pt and MXenes on the nanoprobe can significantly amplify the signals to improve detection sensitivity. In particular, the dual detection system could mutually verify to achieve high accuracy. The aptasensor could also be expanded to rapid analysis of other food-borne pathogens through changing the aptamer on the electrode.

In this work, a fluorescence/localized surface plasmon resonance (Fluorescence/LSPR) dual-readout sensing system that using DNA functionalized gold nanoparticles (AuNPs) as nanoprobe was designed for acetamiprid (ACE) and organophosphorus pesticides (OPs) detection. The ACE detection was based on the fluorescence resonance energy transfer (FRET) between fluorochrome Cy3-labeled aptamer and AuNPs of nanoprobe. The high specificity of ACE allowed Cy3-labeled aptamer to release from nanoprobe, resulting in a significantly fluorescence recovery related to the concentration of ACE. On the other hand, the strategy for OPs detection relied on the acetylcholinesterase (AChE)-mediated oxidative polymerization blocking of dopamine on AuNPs surface and the inhibition of OPs toward AChE. The degree of polymerization of dopamine depended on the concentration of OPs, which led to a tremendous LSPR spectral shift and scattering color change of nanoprobe. The dual-readout sensing system showed great sensitivity and selectivity for ACE and OPs (used chlorpyrifos as model) with a detection limit of 166.7 pg mL−1 and 0.17 fg mL−1, respectively. Moreover, two distinct color changes could be visual recognized to indicate the content of ACE and OPs, which was considered to be a conceivable way for pesticides residues assay. Therefore, this work paved a new avenue for rapid detection of multi-pesticides via a Fluorescence/LSPR dual signal response and visual screening, and hold great potential for noxious substance monitoring.

Based on the signal transduction with a horseradish peroxidase (HRP)-functionalized gold nanoprobe, this work develops a new electrochemical aptasensing method for kanamycin (Kana) detection. The aptasensor was constructed through the hybridization of biotinylated Kana-aptamer at its complementary oligonucleotide strand-modified electrode, followed by intercalating methylene blue (MB) into the formed double-stranded DNA (dsDNA). Then, the streptavidin and high-content HRP functionalized gold nanoparticle probes were bound onto the aptasensor. As the MB-mediated HRP-catalytic reaction could produce sensitive electrochemical signal and the aptamer-biorecognition toward Kana could cause quantitative decrease of MB intercalation and nanoprobe capture, convenient electrochemical signal transduction was achieved. Both the enzymatic reaction and nanoprobe signal amplification greatly enhance the electrochemical signal, offering ultrahigh sensitivity of the method. The MB intercalation into dsDNA not only provides necessary electron mediator for the enzymatic reaction but also simplifies the electrochemical measurement. Under optimal conditions, this method showed a wide linear range over four-order of magnitude with a low detection limit of 0.88 pg/mL. In addition, the aptasensor features high specificity, excellent repeatability and stability as well as satisfactory reliability. Thus it possesses valuable application potentials.

Hydrazine is a probable human carcinogen and exhibits critical damage to living system. Developing an effective method to detect hydrazine in living samples holds great potential for cancer diagnosis, treatment, and management. In this work, we first fabricate a self-assembled micellar nanoprobe for specific recognition of hydrazine in vitro and in vivo in aqueous solution. The novel probe (T-M) contains a triphenylamine fluorophore as a reporter and malononitrile group as the triggered moiety, then we encapsulated T-M into the hydrophobic interior of an amphiphilic copolymer (mPEG-DSPE) and prepared a novel self-assembled micellar nanoprobe: NanoT-M. The nanoprobe exhibits ultra-sensitivity, high selectivity and good biocompatibility. Furthermore, the nanoprobe shows favourable cellular uptaken and was successfully used to detect intracellular hydrazine in living cells.

Current lysosomal H2S-responsive fluorescent probes usually possess notorious aggregation caused quenching (ACQ) phenomenon and suffer from the inevitable background fluorescence signals. To circumvent this problem, we here combined H2S recognizing aggregation-induced emission (AIE) group with photochromic spiropyran moiety to rational design novel photoswitchable AIE nanoprobe (DNBS-DCM-SP) for lysosomal H2S detection with high spatiotemporal resolution. In the presence of H2S, the electron-withdrawing DNBS moiety will deviate from DNBS-DCM-SP via a H2S-induced O S bond cleavage, induced a sensitive turn-on fluorescence response at about 592 nm. The prepared nanoprobe displays good sensitivity (∼5.0 nM), and high specificity (especial against other thiols). In additon, the fluorescence of the H2S-activated AIE nanoprobe (DCM-SP) can be reversibly switched by selective fluorescence resonance energy transfer (FRET) from the AIE fluorophore (DCM) to ring-opened state of spiropyran via alternating UV/visible light irradiation. Moreover, the feasibility of the prepared photoswitchable AIE nanoprobe is also demonstrated by mapping the production of endogenous H2S in living cells as well as reversible dual-color fluorescence imaging.

Alendronate sodium (ALDS) is an important and regularly used medicine in clinical therapy of osteoporosis. In this work, a new analytical method is developed for the detection of ALDS based on a fluorescent platform of copper(II)–mediated silver nanoclusters (AgNCs). Specifically, Cu2+ can selectively bind with DNA-stabilized AgNCs and thus greatly quench their red fluorescence. In the presence of ALDS, their fluorescence can largely recover again owing to the stronger coordination of ALDS with Cu2+. On the basis of such a mechanism, fluorescence “on-off-on” mode of the nanoprobe is applied to detect ALDS in a wide linear range of 800 pM–200 μM, with a detection limit of 100 pM. Compared with previously reported methods, the present approach has significant advantages regard to simplicity, high sensitivity, and a wide detectable concentration range. This method has been successfully applied in ALDS assay in tablets and human body fluids.

The organophosphorus compound (OP) induced inhibition of acetylcholinesterase (AChE) and their reactivation has been monitored using gold nanoprobe. The method is based on the colour change and red shift of localized surface plasmon resonance (LSPR) absorption band of AuNPs in UV–vis region after the addition of acetylthiocholine in presence of AChE. The aggregation of AuNP is induced by the thiocholine (TCh) through Au-S binding and electrostatic force of interactions. The inhibitory attack of OPs at the active serine site of the AChE leads to the decrease in formation of TCh molecule, which consequently, prevents the aggregation of the AuNPs. Conversely, the red shift of LSPR has been regained upon the reactivation of OP inhibited AChE by oximates (2-PyOx−, 4-C12PyOx−) and salicylhydroxamate (SHA). The inhibition protocols of the AChE have been used for detection of OP pesticides. The linear range for determination of OPs was found in range of 0.30–17.30 ng mL−1 with their limit of detection being 0.13 ng mL−1, 0.37 ng mL−1, 0.42 ng mL−1 and 0.20 ng mL−1 for paraoxon, parathion, fenitrothion and diazinon, respectively. The proposed method was found to be simple, sensitive and cost effective for the determination of OPs in real water samples.

Fluorescent nanoprobe has been judiciously tailored after incorporation of nitrogen and sulphur in carbon dots. The synergistic occurrence of sulphur and nitrogen affords outstanding luminescence property and provides recognition sites for specific and selective sensing of acetone (ketone) with an ultra-low limit of detection (7.2 × 10−7 M). This nano probe was successfully endorsed with real biological samples such as human blood and urine. The prepared carbon dots possess very high quantum yield (69.27%), excellent water dispersibility, non-toxic and ultrahigh photostability. Herein, we demonstrate an innovative perspective on the commercialization of carbon dots as a potential substitute to expensive kit for the detection of ketone bodies in human fluids.

A simple and rapid colorimetric approach for Hg2+ detection is achieved by etching silver-coated gold nanobipyramids (Au NBs@Ag nanoparticles) based on the redox reaction between Hg2+ and silver nanoshell of the Au NBs@Ag nanoparticles. The decrease of the silver nanoshell thickness leads to first blue shift and then red shift of the longitudinal localized surface plasmon resonance (LSPR) peak and accompanies a vivid color change. The blue shift is more suitable for colorimetric detection which has the obvious multicolor change from yellow-green to green and then to blue-gray; and could be employed to quantitatively detect the concentrations of Hg2+. This nanoprobe with the longitudinal LSPR peak at 730 nm exhibits a linear range of 0.1–20 μM with a limit of detection (LOD) of 22 nM based on blue shift and has the most obvious color change with the lowest LOD of 0.8 μM by direct observation. In this case, the Au NBs@Ag nanoparticles are gradually etched from the nanorods to nanorices as the Hg2+ concentration increases. Compared with other techniques, this method could avoid tedious procedures and is time-saving. Furthermore, this nanoprobe has good selectivity, and is well demonstrated in real samples with satisfied results.

We present an efficient carbon quantum dots (CQDs)-modified silver nanoparticles (AgNPs) (CQDs-AgNPs) as turn-on fluorescence nanoprobe for monitoring hydrogen sulfide (H2S) in brain microdialysate. The fluorescence of the CQDs-AgNPs probe can be selectively and sensitively turned on by H2S due to the formation of Ag S bonds between AgNPs and H2S and breaking of the Ag N bond between AgNPs and CQDs. Density functional theory (DFT)/time-dependent density functional theory (TD-DFT) investigation were thoroughly conducted on the electronic structures, absorption and emission spectra of CQDs-AgNPs complex as well as the sensing mechanism for hydrogen sulfide. The CQDs-AgNPs fluorescent probe illustrates a wide linear detection range towards H2S from 1 to 1900 nM with the detection limit of ∼0.4 nM. This improved sensitivity, lower limit, along with the high selectivity and fast response toward H2S, makes this CQDs-AgNPs complex successfully monitor H2S basal level in rats without exogenous stimulation, which was calculated to be 3.08 ± 0.10 μM (n = 3). This novel fluorescence probe provides an assay for direct detection of H2S in the cerebral systems and contributes to understand the physiological function and molecular mechanisms of endogenous H2S.

In this work, red-emissive carbon dots (CDs) were prepared through microwave-assisted heating and then conjugated with fluorescein isothiocyanate (FITC) to construct a ratiometric multi-functional nanoprobe (CDs-F) for both pH sensing and biothiols analysis. After coupling with FITC, the as-obtained CDs-F shows both green and red emissions. Based on the pH sensitivity of FITC, the CDs-F can be used for ratiometric pH sensing. On the other hand, the red emission of CDs can be quenched significantly by Ag+. Studies of quenching mechanism demonstrate that Ag+ could coordinate with the functional groups of CDs resulting in the formation of the CDs-Ag+ complex and also charge transfer between the CDs and Ag+. Simultaneous static and dynamic quenching processes impart the maximum quenching. Based on the strong affinity between thiol groups and Ag+, the CDs-F with dual emissions can be used for ratiometric biothiols analysis with the detection limits of tens of nanomole per liter. Furthermore, the strategy has been successfully applied to monitor proton-related enzymatic catalytic reactions and to determine biothiols in fetal bovine serum samples with good recoveries.

Fluorescent carbon dots (CDs) were synthesized through hydrothermal treatment of an easily available fish scales precursor. The as-prepared CDs exhibit good water-solubility, wavelength-tunable fluorescence nature with fluorescence quantum yield of 9%, high photostability and resistance against common ions and biomolecules, thus enables the application as viable fluorescent nanoprobes for detection of pharmaceuticals molecules. The fluorescence of CDs can be efficiently quenched by lidocaine hydrochloride (LH) through static quenching, hence the CDs can serve as a simple and rapid fluorescent probe for determination of LH pharmaceutical. The fluorescent CDs probe demonstrated a wide linear range (0.185–1.295 mmol L−1) and a low detection limit (0.054 mmol L−1). The CDs also demonstrates low cytotoxicity, which enables the accurate fluorescent detection of LH in human serum.

In this article, we reported a dual emissive multicolorful fluorescent-nanoprobe which was composed of gold nanocluster (BSA-Au NCs) and carbon dots (CDs) with a certain proportion, i.e. Au NCs-CDs. The dual emissive Au NCs-CDs showed pink fluorescence under UV light, and the dual emission peaks at 625 nm and 444 nm were corresponded to the existence of Hg2+ and Cr6+ respectively. The fluorescence color transformed from pink to blue when in presence of Hg2+. The blue fluorescence emission of CDs selectively quenched by Cr6+, whereas the red fluorescence of BSA-Au NCs was stable against Cr6+, which can be treated as internal reference. The difference response of the two emissions to Hg2+ and Cr6+ resulted in a distinguished fluorescent color change, which can be noticed by the naked eyes clearly. When the Hg2+ and Cr6+ were exposed to the Au NCs-CDs simultaneously, the dual-emission of the Au NCs-CDs were all reduced and exhibited the complete quenching of the pink emission. The detection limits for Hg2+ and Cr6+ were 1.85 nM and 5.34 nM, respectively. Significantly, it was successfully applied to determine the existence of Hg2+ and Cr6+ in real samples, which offered the advantages of simplicity, environmentally friendly and cost saving efficiency.

A facility fluorescent sensor was fabricated for highly selective and sensitive detection of Fe3+ relying on red emissive carbon dots (RCDs) used as the target sensitive fluorophore. Fluorescence quenching are attributed to the strong coordination interaction between the target ions and the phenolic hydroxyl groups on the surface of RCDs. Interestingly, the fluorescent nanoprobe also showed great potential in detection of bovine serum albumin (BSA), attributed to the existence of Fe3+ ions. Serum albumins are the most abundant proteins spreaded throughout the circulatory system of all kinds of organisms, which play a crucial role in the process of metabolism. More importantly, the ratiometric fluorescent probe is easy to fabricate by mixturing blue emissive carbon dots (BCDs) with RCDs together, the fluorescence intensity of RCDs can be obviously quenched by Fe3+ ions or BSA under a single excitation wavelength, but that of BCDs is weakly changed, leading to the ratiometric fluorescence response with a good linear wider range of 0–400 μM and 0–320 μM, respectively. This ratiometric probe has also successfully been applied in real samples, that are cow urine and lake water, and observed to be almost no interference in the detection of Fe3+ ions.

Currently, the bio-immobilization methods displayed great potential for the removal and recycle of highly toxic metals depending on their gentle and orderly regulated cellular environment. Herein, we have presented a facile and eco-friendly strategy for bio-immobilizing cadmium (Cd) ions and to harvest CdSe quantum dots (QDs) using microalgae cells as bio-reactors. The production process has good environmental benefits for recycling hazardous Cd metal. The biosynthesized CdSe QDs exhibited superior optical properties, good water-solubility, high crystallinity structure, and were monodispersed sphere nanoparticles with approximate range of 5–6 nm in size, clearly comfirmed by the inversed fluorescent microscope, Ultraviolet-visible, photoluminescence, transmission electron microscopy analyses and so on. Owning to their fluorescence quenching effect, the as-obtained CdSe QDs could be deemed as an effective fluorencent nanoprobe for imatinib detection. The linear range for imatinib was calculated to be from 10.43 μg mL−1 to 417.30 μg mL−1 with a low detection limit of 0.014 μg mL−1. More strikingly, the possible formation mechanism of CdSe QDs in algal cells was preliminarily speculated that could be related with the intracellular GSH, which could provide new insights for the possibility for environmental transformation of poisonous metals to fluorescent QDs.

Herein, we utilized aconitic acid (AA) as the precursor for preparing carbon dots (AA-CDs) by a facile hydrothermal reaction, and the resulting AA-CDs exhibited bright blue fluorescence with an absolute quantum yield of 56.5% in aqueous solution. Preliminary experiments showed that the prepared AA-CDs without further surface passivation or modification could selectively interact with folic acid (FA), resulting in significant fluorescence quenching. Based on this, a sensitive method for FA analysis was developed with a detection limit of 40 nM (S/N = 3), which was then successfully applied for the detection of FA in food and pharmaceutical samples with the average recoveries of 95.0–105.3%. Furthermore, a weak fluorescent nanoprobe (FA-AA-CDs) was fabricated based on the conjugated interaction of FA and AA-CDs, and its feasibility was evaluated as a fluorescence turn-on nanoprobe for targeted imaging of cancer cells using Hela, SMMC-7721, and A549 cells as models that expressed different levels of folate receptors (FRs) on the cell surface. The results exhibited that the fluorescence intensity of these cells was in accordance with their FRs expression levels, testifying its potential of FA-AA-CDs for targeted imaging of cancer cells. Subsequently, the internalization mechanism of FA-AA-CDs into cells was elucidated via receptor-mediated endocytosis using control experiments.

Herein we combine the enzyme-nanoprobe induced biomineralization of cupric subcarbonate with a sensitive copper chromogenic reaction to develop an ultrasensitive colorimetric immunosensing method. The nanoprobe was prepared through the surface assembly of signal antibody and high-content urease on the nanocarrier of gold nanoparticle (Au NP). Upon sandwich immunoreaction at a magnetic bead (MB)-based immunosensing platform, the analyte of carcinoembryonic antigen and the Au NP/urease nanoprobe were quantitatively captured onto the MB surface successively to form an immunocomplex. The enzyme reaction of the nanoprobe resulted in the catalyzed hydrolysis of the urea substrate to produce large amounts of OH− and HCO3−. These ions were further combined with added Cu2+ to form the biomineralization of cupric subcarbonate rapidly on the immunocomplex. Based on the acid-release of Cu2+ from the biomineralized products for the chromogenic reaction, a red complex was obtained and employed for the ultrasensitive colorimetric signal transduction. Under the optimum conditions, a linear range over five orders of magnitude was obtained with a low detection limit of 0.45 pg/mL. In addition, this method features low cost, rapid and convenient operation as well as satisfactory reproducibility, stability and accuracy. It thus owns great potentials for practical applications.

The silica nanoparticles (SiO2NPs) conjugated with azidocoumarin (Cy-N3) was applied for the selective and sensitive H2S detection, even when H2S was present in 1000-fold excess of other bio thiols and ions. In the silica nanoprobes, azide in the Cy-N3 group acted as the recognition element, and the probe was biocompatible. The nanoprobe displayed blue emission at 456 nm and excitation at 367 nm. After introducing H2S into the probe solution, the fluorescent intensity at 456 nm increased linearly as a function of H2S concentration (correlation coefficient, 0.9970), and the limit of detection was 6 nM. The enhanced fluorescent emission intensity was due to H2S-mediated reduction of the electron-withdrawing azide into electron-donating amine. The SiO2NPs@Cy-N3 and its reaction products with H2S (SiO2NPs@Cy-NH2) were characterized by 1H NMR and TEM. The probe also showed low cytotoxicity and could trace endogenous H2S in physiological pH. We therefore then successfully utilized it to detect H2S in living PC3 cells. The probe was also successfully employed for detection of H2S gas using Whatman papers coated with SiO2NPs@Cy-N3.

The selective detection of 4-nitrophenol (4-NP) is deemed important from an environmental and biochemical point of view. Herein, the synthesis of highly fluorescent carbon nanodots (CNDs) from apple seeds, as a carbon and nitrogen source is described, using a single-step pyrolysis method. The synthesized nitrogen-doped CNDs emit intense blue fluorescence, which can effectively be quenched by 4-NP, via the Forster resonance energy transfer (FRET) mechanism. The ‘green’ CNDs are properly characterized and examined for their fluorescent and stability properties. The CNDs are proved to be a successful sensing nanoprobe for the development of an analytical method towards the sensitive and selective detection of 4-NP in environmental water samples and human urine. The high availability and low value of the precursor along with the low cost of synthesis and analysis and the selective sensing are the major advantages of the proposed method. The wide linear range (0.05–53.0 μM), the low limit of detection (13 nM) and the acceptable sample recoveries (from 101 to 112%) render the proposed sensing method an improved alternative to previously proposed methods. Finally, the CNDs are explored for cell imaging in three cell lines, with excellent biocompatibility and negligible cytotoxicity, suggesting their great potential in bioimaging and other biosensing applications.

Overproduction of reactive oxygen species (ROS) results in oxidative stress, which is closely associated with pathogenesis of many diseases. Visualized detection of ROS in situ enables deeper insight into the mechanisms that underlie such pathological and physiological processes. Among reactive species, selective detection of hydroxyl radical is the most challenging, due to high aggression and short life time of this specie. In this regard, we have developed a sensitive and selective ratiometric fluorescence nanoprobe for detection of hydroxyl radical. This probe is based on use of GUMBOS (a Group of Uniform Materials Based on Organic Salts) that are derived from 1,1′-diethyl-2,2′-cyanine iodide and 1,1′-diethyl-2,2′-carbocyanine iodide. Each GUMBOS exhibit different reactivity towards reactive species. Without any chemical linkage, these two GUMBOS were combined into a single nanomaterial to produce a ratiometric fluorescent sensing profile through Forster resonance energy transfer. This cyanine-based ratiometric nanoprobe exhibited high selectivity for the hydroxyl radical in comparison to other ROS, including superoxide anion, singlet oxygen, hydrogen peroxide, and peroxynitrite. Furthermore, detection of hydroxyl radical was successfully demonstrated by use of these binary nanoGUMBOS in vitro using hormone-independent human breast adenocarcinoma cells (MDA-MB-231).

A specific targeting, biocompatible, magnetic nanoprobe for bioimaging of pancreatic cancer cell lines was developed by simple three-step route in aqueous solution. Herein, the nanocomposite consists of superparamagnetic iron oxide core having gold nanocluster adsorbed around it through electrostatic attraction. The Au NC corona layer is further conjugated with positively charged erlotinib. The Fe3O4 nanoparticles ensures the magnetic enrichment, Au NCs exhibit intense red fluorescence property and erlotinib act as a specific targeting agent for pancreatic cancer cells. The resultant targeted nanoparticles had a diameter of 24 ± 2.5 nm with relatively high fluorescence life (τav = 1.17 μs @ λem = 640 nm) and can kill EGFR over expressed pancreatic cancer cells. Confocal laser scanning microscope images of the normal cells (L-929) and pancreatic cancer cells (PANC-1) treated with probe is conducted. The results shows that the morphology of the normal cells remains intact attesting its non toxicity while PANC-1 which is over expressed with EGFR exhibit cytotoxicity towards the probe proving the potential theranostic ability of the nanocomposite.

A novel graphene oxide (GO)-based pH sensor was designed and prepared through covalently attaching a zwitterionic betaine molecule onto a GO surface. This betaine-modified GO (BMGO) exhibited high water solubility and low toxicity. In aqueous media, BMGO displayed increased fluorescence in acidic conditions and decreased fluorescence in basic conditions. BMGO possesses a pH sensing range from 4 to 12 with excellent reversibility, quick response and high stability. With its high sensitivity and robustness, BMGO can be used to monitor the pH of intracellular contents, as demonstrated through cell imaging.

Alkaline phosphatase (ALP) is an essential enzyme in phosphate metabolism and widely distributes in mammalian body fluids and tissues. So far, various fluorescent probes for ALP have been well developed, but some disadvantages such as short emission wavelength and low photostability restrict their biological application. Herein, a near-infrared (NIR) fluorescent nanoprobe based on infinite coordination polymer nanoparticles (CyOH@Tb-GMP) is constructed for endogenous ALP activity assay. The characteristics of the nanoprobe are as following: (1) The fluorescence emission of the nanoprobe is at 718 nm belonging to NIR region, which is suitable for bioimaging. (2) The nanoprobe displays better photostability than common NIR dyes such as ICG as well as CyOH. (3) The nanoprobe exhibits high sensitivity for ALP activity with a 7.5-fold fluorescence enhancement when 2.5 U/mL ALP is added. (4) The NIR nanoprobe is employed for monitoring endogenous ALP activity in various biological samples such as cell, tissue and mice with satisfactory results.

Nowadays, sole recognition of targeted species is not sufficient to quantify or recover it from environmental samples. Therefore, current challenge in the management of crucial species is to improve or design sensing probes which are able to recognize, quantify as well as recover it from various assays. Herein, a Schiff base chemosensor SB has been modulated to SB-Silt after incorporating hydrolysable units for its covalent grafting on silica surfaces. Interestingly, despite fluorogenic insensitivity of SB towards metallic species, SB-Silt was found to be highly efficient for the recognition and quantification of Zn2+ ions. Furthermore, functionalization of nanosilica with SB-Silt produced a multi-functional nanoprobe SB@SNPs for monitoring Zn2+ ions. The ‘turn ON’ fluorescence emission in SB-Silt and SB@SNPs (at 437 nm and 457 nm, respectively) in the presence of Zn2+ ions enabled the detection upto 6.8 nM and 0.17 μM (LODs), respectively. The maximum adsorption capacity (Qm) of SB@SNPs for Zn2+ ions was determined to be 167.2 mg g−1. Moreover, the SB-Silt-Zn2+ conjugate (formed by the interaction of SB-Silt and Zn2+ ions) exhibited a complete quenching of fluorescence (at 437 nm) accompanied with continuous red shifting of emission wavelength to 517 nm in the presence of hydrogen phosphate (upto 4 equiv.). Overall, the developed material is highly efficient, sensitive, selective, reusable and easily separable, and hence can be used as a multifunctional nanoprobe.

Here, a sandwich-type electrochemiluminescence (ECL) immunosensor for ultrasensitive determination of HBsAg was designed based on signal amplification with dendrimeric-quantum dots structures. First, the primary antibody of HBs (Ab 1 ) was immobilized on the surface of the carboxyl-modified magnetic nanoparticles (MNPs). Then, the PAMAM dendrimer with many amine functional groups was employed as the carrier for immobilizing CdTe@CdS quantum dots (QDs) and the secondary antibody (Ab 2 ) which can amplify the ECL signal of QDs significantly and improve the sensitivity of the proposed method. Dendrimer increasing loading of CdTe@CdS-Ab 2 labels, while ECL response from CdTe@CdS QDs enhanced 4 folds compared to the unamplified protocol. Furthermore, MNPs enhances the electron transfer between the nanoprobe and the electrode and also, their large surface area leads to immobilize more Ab 1 . Under the optimal conditions, the constructed immunosensor showed a wide linear range from 3 fg mL −1 to 0.3 ng mL −1 with the detection limit of 0.80 fg mL −1 (S/N ratio of 3) for HBsAg detection. The proposed ECL immunosensor exhibited good analytical performance and excellent stability and it was applied for HBsAg detection in human serum samples with satisfactory results.

In this paper, we developed a simple, rapid, selective and colorimetric method to detect iodide (I−) by etching silver-coated gold nanobipyramids (Au NBs@Ag nanostructure) in the presence of Cu2+. The detection is based on the reaction that Cu2+ could oxidize I− into I2, which sequentially etches the Ag shell of Au NBs@Ag nanostructure. When the Ag coating is thick and the Au NBs are buried in Ag nanorods, the decrease of the Ag shell thickness and aspect ratio results in the blue-shift and intensity decrease of the longitudinal localized surface plasmon resonances (LSPR) peak. The blue-shift and intensity decrease of the longitudinal LSPR peak have been employed to quantificationally detect the concentration of I−. The linear range of the detection could be improved by increasing the concentration of Cu2+ and reaction time. Under the optimized conditions, both the blue-shift and intensity decrease of the longitudinal LSPR have linear correlation with the concentration of I− in the range of 1.0–15 μM. When the Ag coating is very thin, the etching of the Ag shell results in the red shift of the LSPR in the visible range, which further leads to the color of the colloid change from blue to pink. The etching-induced color change of the colloid also depends on the concentration of I−, which enables the visual detection of I−. Compared with other techniques, this method could facilitate multi-model quantitative detection of I− without any sophisticated instrument. Interference studies and real samples test show that I− could be specifically detected in dried kelp using this bimetallic optical nanoprobe.

A nanotheranostic system integrating activatable photoactivity and dual targeting modalities is significant for bioimaging and biomedicine. In this study, a dual-targeting and tumor microenvironment responsive nanoassembly for imaging of HAase and PDT of tumor was developed. The synthesized water-soluble cationic porphyrin act as both the mitochondrion targeting photosensitizer and crosslinking agent to trigger the formation of HA-Mito TPP nanoparticle via the electrostatic interaction with hyaluronic acid. The nanoassembly could be efficiently endocytosed into targeted tumor cells and activated both fluorescence signal and enhanced PDT effect by highly expressed HAase. In vitro experiments suggested that the reported assay had desirable selectivity and excellent anti-interference for HAase quantitative analysis. The live cell studies showed the HA-Mito TPP had obviously enhanced PDT efficiency and caused mitochondria damage. Therefore, the developed dual-targeting nanotheranostic system provide a promising platform for bioanalysis and imaging guided photodynamic therapy.

As a universal second messenger, Ca2+ plays an important role in many cellular processes. In this work, we have developed a novel dual-mode nanoprobe, including "turn on" fluorescence and "turn off" SERS, which can be used for sensitive and selective Ca2+ determination. The proposed nanoprobe combines gold nanostars (AuNSs) and DNAzyme (recognition element), among which AuNSs are used to quench fluorescence and enhance Raman signals. When the substrate chain modified with Cy5 hybridizes with the enzyme chain on the surface of AuNSs, a Ca2+-specific DNAzyme is formed. At this time, the fluorescence is quenched and the SERS signal is strong. With the help of Ca2+, Cy5-labeled substrate chain is cleaved and released from the surface of AuNSs, which leads to the reduction of the SERS signal and the recovery of fluorescence signal. The proposed strategy is also successfully used to monitor Ca2+ in the process of T-2 toxin-induced apoptosis. This is the first report of the simultaneous fluorescence-SERS imaging technique using DNAzyme to detect Ca2+ in cells. The proposed nanoprobe combines the advantages of SERS and fluorescence and has good versatility in various cell lines, which is helpful to better understand the role of Ca2+ in cellular pathways.

In this study, highly red emissive mercury-doped zinc selenide quantum dots (Hg-doped ZnSe QDs) were prepared by facile mixing of Hg2+ and ZnSe QDs. Further, a ratio fluorometric technique was designed for ultrasensitive detection of alkaline phosphatase (ALP) based on in situ generation of Hg-doped ZnSe QDs and quinoxaline derivative (QXD). Under the catalysis of ALP, ascorbic acid (AA) was generated from ascorbic acid 2-phosphate, and the as-generated AA underwent a redox reaction with Hg2+ to produce dehydroascorbic acid (DHA) and Hg, which resulted in significant suppression of red fluorescence at 635 nm because the lack of Hg2+ blocked the formation of Hg-doped ZnSe QDs. Furthermore, the occurrence of reaction between DHA and o-phenylenediamine produced fluorescent QXD, which caused the significant enhancement of blue fluorescence at 436 nm. Thus, a novel ratio nanoprobe utilizing Hg-doped ZnSe QDs and QXD as dual fluorescent reporter was fabricated for measuring ALP activity. The linear ranges were 0.001–0.02 U L−1 and 0.02–1.4 U L−1 with the detection limit of 0.001 U L−1. Furthermore, the nanoprobe enabled visual detection of ALP activity when exposed to ultraviolet light, and it exhibited satisfactory results for measuring ALP activity in human serum. This study provides a valuable method for ALP-related disease diagnosis and drug screening.

The development of sensitive and convenient strategies for monitoring intracellular caspase-1 activity is of great significance. Herein, a novel fluorescence nanoprobe for caspase-1 activity determination was constructed based on surface energy transfer (SET) between red-emissive carbon dots (RCDs) as a donor, and Au nanorods (AuNRs) as an acceptor. The donor/acceptor pair were covalently bridged with a peptide containing a caspase-1 cleavage site (YVAD) at middle. The stability and dispersivity of the AuNR-Pep-RCD nanoprobe was realized/enhanced by pretreating the AuNRs with PEG-SH. Active caspase-1 cleaves the YVAD site, releasing RCDs and recovering the fluorescence. Synergic effect of the red-emission, sensitive and selective cleavage, and excellent SET efficiency contribute to the nanoprobe with high sensitivity and selectivity, especially in biological samples. More importantly, the nanoprobe can be uptaken by living cells, capable of in-situ intracellular caspase-1 activity imaging. The fluorescence recovery is linearly correlated with caspase-1 activity in the range of 5‒300 ng·mL−1 (2.5 × 10−5‒1.3 × 10−3 U·mL−1), with a limit of detection of 1.76 ng·mL−1 (8.8 × 10-6 U·mL−1). In particular, the fluorescence nanoprobe can accurately detect caspase-1 activity in cells extract, and sensitively probe the caspase-1 activation treatment and inhibition treatment for the intracellular caspase-1 activity levels.

Although various strategies have been developed in cancer theranostics, it’s still a great challenge to achieve a sensitive diagnosis and specific treatment of cancer. Herein, a theranostic nanoprobe (PDAD@F68-HA-DOX) has been successfully fabricated through self-assembly. Under the stimulus of hyaluronidase (HAase), ratiometric fluorescent feedbacks would be received through this FRET-based nanoprobe, exhibiting predominant selectivity and sensitivity. Compared with other analytical approaches, this FRET-based probe with suitable detection limit and linear range could be favorable for the determination of target enzyme. Moreover, it is also able to differentiate tumor cells from normal cells by labeling them with different fluorescence colors. More importantly, this theranostic system could be activated to accomplish specific release of chemotherapeutic drug in lesion areas, resulting in discriminative cytotoxicity to tumor and normal cells. Apparently, this versatile nanoprobe has exhibited great potentials in the early diagnosis and treatment of cancer.