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DNA nanotweezers (DTs) are reversible DNA nanodevices that can optionally switch between opened and closed states. Due to their excellent flexibility and high programmability, they have been recognized as a promising platform for constructing a diversity of biosensors and logic gates, as well as a versatile tool for molecular biology studies. In this review, we provide an overview of biosensing applications using DTs. First, the design and working principle of DTs are introduced. Next, the signal producing principles of DTs are summarized. Furthermore, biosensing applications of DTs for varying targets and purposes, both in buffers and complex biological environments, are highlighted. Finally, we provide potential opportunities and challenges for the further development of DTs.

Fe single atoms immobilised on N- and P-codoped porous honeycomb-like carbon (Fe–N4/NP-PHC) with abundant accessible active sites produce impressive electrocatalytic performance towards oxygen reduction reaction.

An ingenious strategy with the integration of a zwitterionic peptide into a two-photoelectrode system was reported to construct an advanced photoelectrochemical immunosensing platform. The strategy has endowed the platform with both excellent photoelectric properties and an antifouling ability, and was capable of accurate and sensitive detection of target biomarkers in biological specimens.

Accurate and sensitive detection of targets in practical biological matrixes such as blood, plasma, serum, or tissue fluid is a frontier issue for most biosensors since the coexistence of both potential reducing agents and protein molecules has the possibility of causing signal interference. Herein, aiming at detection in a complex environment, an advanced and robust peptide-based photocathodic biosensor, which integrated a recognition peptide with an antifouling peptide in one probe electrode, was first proposed. Selecting human chorionic gonadotropin (hCG) as a model target, the recognition peptide with the sequence PPLRINRHILTR was first anchored on the CuBi2O4/Au (CBO/Au) photocathode and then the antifouling peptide with the sequence EKEKEKEPPPPC was further anchored to generate an antifouling biointerface. The peptide-based photocathodic biosensor demonstrated excellent anti-interference to both nonspecific proteins and reducing agents because of the capability of the antifouling peptide. It also exhibited good sensitivity owing to the utilization of the recognition peptide rather than an antibody probe. This peptide-integrated method offers a new perspective for practical applications of photocathodic biosensors.

β-Cyclodextrin (β-CD) modified silver nanoparticles (AgNPs), denoted as β-CD/AgNPs, were prepared by a simple one-pot method. Due to the inherent chirality of β-CD, the developed β-CD/AgNPs exhibited higher affinity toward l-tyrosine (l-Tyr) than d-tyrosine (d-Tyr), leading to serious aggregation of AgNPs in the presence of l-Tyr. Consequently, the l-Tyr induced aggregation of AgNPs can result in signal amplification in the differential pulse voltammograms (DPVs) of l-Tyr, which can be applied for the electrochemical chiral discrimination of the Tyr enantiomers. Other chiral amino acids including tryptophan and phenylalanine can also be successfully discriminated with the β-CD/AgNPs, suggesting high universality of the developed chiral sensor.

An ultrasensitive electrochemiluminescence (ECL) biosensor was developed based on MIL-53(Al)@CdS QDs and SiO2@AuNPs for trichlorfon detection. Metal–organic frameworks (MOFs) were used as a loading platform that provided a large surface area to load targets and modified materials onto the electrode. At the same time, SiO2@AuNPs loaded plenty of AuNPs which effectively increased the ECL resonance energy transfer between the CdS QDs, so that the ECL signal was strongly quenched and resulted in an amplified response. In the range of 10−11–10−4 M, the ECL response showed a linear relationship with the concentration (logarithm) of trichlorfon, and the detection limit was 5.1 × 10−12 M (S/N = 3). When the biosensor was applied to detect trichlorfon in lettuce, broccoli, cucumber, and chives, the recoveries obtained from the spiked samples were 97%–105%, 102%–104%, 100%–104%, and 98%–104%, respectively. Thus, this novel ECL biosensor has potential applications for the analysis of trichlorfon in food samples.

Nucleic acid lateral flow sensing has drawn great research attention since it has the advantages of being simple, rapid, and cost-effective. However, considering the trace amounts of the nucleic acid targets, its sensitivity is still limited. Although enormous efforts have been devoted to enhancing its sensitivity, developing a simple lateral flow sensing platform with high sensitivity remains challenging. We report a novel lateral flow microRNA-21 biosensing platform based on a portable surface enhanced Raman scattering (SERS) reader coupled with a catalytic hairpin assembly signal amplification strategy. Hairpin DNA probes were anchored on Au@Ag nanotags, and the presence of microRNA-21 triggered the formation of numerous double-stranded DNAs along with the exposure of the biotin groups. By this means, the target was recycled and signal amplification was achieved. The Au@Ag nanoprobes with exposed biotin can be captured on the test line via its interaction with streptavidin. By scanning the strip with a portable SERS reader, the sensitive quantification of microRNA-21 was realized with a detection limit as low as 84 fM. The proposed strategy was employed to detect the target in a serum sample, demonstrating its great potential in amplified point-of-care biosensing for clinical diagnosis.

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

Rabies is caused by the infection of Rabies virus, it leads to fatal encephalitis, developing a highly sensitive and specific detection method for Rabies virus remains a challenge. Herein, we report an electrochemiluminescence (ECL) biosensor for Rabies viral RNA based on dual-signal amplification and DNA nanotweezers (DTs). Dual-signal amplification process includes target binding induced isothermal amplification and CRISPR-based amplification. In the presence of target RNA, two assisted probes simultaneously hybridized with it to trigger isothermal amplification with the help of polymerase and nicking enzyme. This process generated a large amount of single-stranded DNA (ssDNA) as products. The products hybridized with CRISPR RNA to activate the trans-cleavage activity of Cas12a to indiscriminately cleave predesigned single-stranded trigger (ST) strands. After mixing the cleavage products with DTs and hemin molecules, DTs cannot be closed by cleaved ST strands to capture hemin to the electrode to quench the ECL signal. Therefore, the higher concentration of the target, the stronger intensity of the ECL signal. The detection limit is as low as 2.8 pM and the detection range is from 5 pM to 5 nM with excellent specificity and stability. The proposed method provides a promising strategy for Rabies detection, and can be easily adapted to other analytes via reasonable design as a valuable and versatile tool in bioanalysis.

An efficient signaling on-off mechanism was first proposed by integrating exciton-plasmon coupling and exciton energy transfer into cathodic PEC bioassays. This signaling on-off mechanism has endowed the cathodic PEC biosensor with powerful capability for ultrasensitive and specific detection of target DNA.

As nonspecific adsorption or biofouling has obvious side effects on the selectivity, it is a great challenge for cytosensors to detect target cells in practical biological samples. In this study, we first propose the design and synthesis of an antifouling photoelectrode. The antifouling photoelectrode not only has the desired photocurrent response, but also possesses an unexpected antifouling capability of resisting nonspecific adsorption of biomolecules. Herein, the PEDOT-HPG/SnS/ZnO-NT antifouling photoelectrode was formed and a robust photoelectrochemical cytosensor with enhanced sensitivity and selectivity has been demonstrated.

Currently, one of important research directions of photoelectrochemical (PEC) bioanalysis is to exploit innovative photoactive species and their elegant implementations for selective detection and signal transduction. Different from existing candidates for photoelectrode development, this study, exemplified by the cationic dipeptide nanoparticles (CDNPs), reports the first demonstration of self-assembled peptide nanostructures (SAPNs) for the PEC bioanalysis. Specifically, the CDNPs were prepared as representative materials and then immobilized onto the indium tin oxide (ITO) electrode for the PEC differentiation of several commonly involved biomolecules such as ascorbic acid (AA) and l-cysteine. Significantly, the experimental results disclosed that the CDNPs possessed unique photocathodic responses and good analytical performance toward AA detection in terms of rapid response, high stability, and excellent selectivity. This work demonstrates the great potential of the large SAPN family for the future PEC bioanalysis development and has not been reported to our knowledge.

A promising electrode with three-dimensional (3D) AuNPs/ZnO/Cu2O heterojunction nanowires (NWs) was developed and applied as photocathode for sensitive photoelectrochemical (PEC) immunoassay toward carcinoembryonic antigen (CEA, Ag). Firstly, Cu2O NWs were grown in situ on a Cu foil substrate to provide large specific surface area. After the modification of ZnO layer on the Cu2O NWs, the ZnO/Cu2O heterojunction structure was formed, which can increase the harvest of light energy and play a role in charge separation and transport. With further modification of gold nanoparticles (AuNPs), the good electric conductivity of the AuNPs would induce enhanced charge separation between Cu2O and ZnO. Thus, the photocurrent response of the prepared 3D AuNPs/ZnO/Cu2O NWs photocathode was significantly improved by synergistic effects of each element in the 3D structure. As a result, the fabricated cathodic PEC immunosensor exhibited high sensitivity with a low detection limit of 0.36 pg/mL (S/N = 3) for CEA detection. Furthermore, good specificity and well anti-interference capability toward real sample detection was achieved.

Photoelectrochemical (PEC) sensing and biosensing have received much attention owing to their great potential for future biomolecular detection. The use of an appropriate photoelectrode is essential for PEC sensing and biosensing. Among the numerous semiconductors, many Bi-based ones are of great interest due to their high visible-light-responsivity, easy fabrication and good biocompatibility. Currently, the impetus for advanced Bi-based PEC sensing and biosensing has grown rapidly, as demonstrated by increased scholarly reports. This review introduces the state-of-the-art type and properties of Bi-based photoelectrodes, as well as their analytical applications toward various biomolecules, gas biomolecules and metal ions etc. The future prospects in this area will also be discussed based on our own opinions.

Cathodic photoelectrochemical (PEC) bioanalysis has been drawing more attention in recent years due to the advantages of excellent anti-interference capability. l -cysteine (Cys) is an essential sulfur-containing amino acid and has been intensively addressed as targets in previous anodic PEC bioanalysis. Herein a novel and simple cathodic PEC l -cysteine (Cys) sensor is reported, on the basis of facile electrochemical fabrication of CuO/Cu2O heterojunction photocathode and the selective interaction between the copper and Cys via the formation of Cu S bond. The as-prepared sensor exhibited excellent biosensing performance in terms of high sensitivity, selectivity and stability. In such a sensor, the binding-induced decrease of cathodic photocurrent can be related to target concentration from 0 and 1.5 μM. This cathodic PEC Cys sensor exempted the use of expensive equipment and required no laborious sensor development procedures. We hope it can inspire more interest for further development of simple and practical PEC sensor toward important biomolecules.

Previously reported photoelectrochemical (PEC) cytosensing commonly relied on the use of photoelectrodes as both signaling sources and platforms to accommodate the biorecognition events. In such a design, the side reaction between photoelectrodes and potential reductive species in the biological media as well as the interplay between the photoelectrodes and biomolecules will inevitably impair the performance of the corresponding PEC cytosensors. Herein, we presented a facile and efficient PEC cytosensor by separating capture probe from the photoelectrode. The system is operated upon by using a ternary heterostructured photoanode to provide an evident and stable photocurrent signal, an aptamer-based biocathode for recognizing and capturing the target cells, and the corresponding signal reduction from the cell-induced steric hindrance effect. Exemplified by human breast cancer cells (MCF-7), the proposed system realizes the separation of the signaling photoanode and the sensing biocathode toward a sensitive and selective self-powered PEC MCF-7 cytosensor. This work reports a new PEC cytosensing protocol, and it is expected to attract more interest in the research of high-performance PEC cytosensing.

This work reports the innovative design and application of a three-dimensional (3D) TiO2@Cu2O@nickel foam electrode synergized with enzyme catalysis toward the proof-of-concept study for oxygen-ind...

Photoelectrochemical (PEC) DNA bioanalysis has been drawing more attention in recent years due to the advantages of PEC technique and the vital importance of DNA biomolecules. DNAzymes are unique catalytic nucleic acid molecules that are capable of catalyzing specific biochemical reactions. Using the target-binding-induced conformation change of hairpin DNA probe to hemin/G-quadruplex-based DNAzyme and a plasmonic Au@Ag nanoparticles (NPs)/TiO2 nanorods (NRs)/fluorine-doped tin oxide (FTO) heterostructured photoelectrode, this work reported a novel and sensitive PEC DNA analysis on the basis of a DNAzyme-stimulated biocatalytic precipitation (BCP) strategy. In such a design, the BCP-induced decrease of plasmonic photocurrent can be related to the target-responsive formation of DNAzymes and thus be monitored to assay the target DNA from 0.1 and 100 nM. In brief, with a plasmonic photoelectrode and a hairpin probe, this work reported a general plasmonic DNAzyme-based PEC DNA analysis, which could also be easily extended to aptasensing toward numerous targets of interest.

Energy transfer (ET) in photoelectrochemical (PEC) bioanalysis is usually generated between noble metal nanoparticles (NPs) and traditional inorganic quantum dots (QDs). Using the innovative polymer dot (Pdot)-involved ET, this work reports the first signal-on and cathodic PEC bioanalysis toward telomerase (TE) activity in cell extracts. Specifically, the sequential binding of capture DNA (cDNA), telomerase primer sequence (TS), and Au NP-labeled probe DNA (Au NP-pDNA) on the electrode would place the Au NPs in close proximity of the Pdots, leading to obvious quenching of the cathodic photocurrent. The subsequent extension of the TS by TE in the presence of deoxyribonucleoside triphosphates (dNTPs) would then release the Ag NP-pDNA from the electrode, leading to the recovery of the photocurrent. On the basis of the Au NP-induced photocurrent quenching and the recovery of Pdots, a sensitive biosensor could thus be developed by tracking the photocurrents to probe the TE activity. This strategy allows for signal-on and cathodic PEC bioanalysis of TE, which can be easily extended for numerous other targets of interest. We believe this work could offer a new perspective for the rational implementation of Pdot-involved ET for advanced PEC bioanalysis.

Porphyrins modified inorganic semiconductors have been paid more attention as a platform in nanomaterials, due to the fast electronic transfer from synergistic effect. Meso-tetrakis(4-chlorophenyl)porphyrin functionalized CuFe2O4/SiO2 nanocomposites (TClPP-CuFe2O4/SiO2) were prepared by a simple method and found to exhibit the higher peroxidase-like activity, compared with that of CuFe2O4/SiO2 without porphyrin. The TClPP-CuFe2O4/SiO2 nanocomposites can effectively catalyze the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to give a blue product (oxTMB) only in 3 min, which can be conveniently distinguished by the naked eye. Notably, the optimal response temperature was 25 °C (room temperature), lower than that of most of nanomaterials as peroxidase mimics, which is in favor of practical application. Based on the fast response as well as the peroxidase activity of TClPP-CuFe2O4/SiO2, a simple, sensitive, selective, colorimetric method was proposed for detection of H2O2 over a range of 8 to 80 μM with a detection limit of 1.02 μM. Furthermore, the system including TClPP-CuFe2O4/SiO2, glucose oxidase(GOx) and the substrate (TMB), provided a colorimetric sensor for glucose in the range of 5 - 100 μM with a detection Limit of 3.62 μM.

Photoelectrochemical (PEC) bioanalysis is a newly developed exquisite methodology for innovative biomolecular detection. Photocathodes made by p-type semiconductors have different photoelectric properties from that of n-type semiconductors-based photoanodes. Due to their obvious advantages and potentials, the integration of PEC bioanalysis and photocathodes has opened almost unlimited possibilities for elegant cathodic PEC bioanalysis. Currently, the impetus for advanced cathodic PEC bioanalysis has grown tremendously as demonstrated by increased research papers. Using illustrative examples, this review discusses specifically on this topic, with the aim to cover the basic concept, major signaling strategies, the state of the art in this field, and the future prospects based on our own opinions.

This Letter reports a novel synthetic methodology for the fabrication of three-dimensional (3D) nanostructured CdS@carbon fiber (CF) networks and the validation of its feasibility for applications as a general platform for photoelectrochemical (PEC) bioanalysis. Specifically, 3D architectures are currently attracting increasing attention in various fields due to their intriguing properties, while CdS has been most widely utilized for PEC bioanalysis applications because of its narrow band gap, proper conduction band, and stable photocurrent generation. Using CdS as a representative material, this work realized the innovative synthesis of 3D CdS@CF networks via a simple solvothermal process. Exemplified by the sandwich immunoassay of fatty-acid-binding protein (FABP), the as-fabricated 3D CdS@CF networks exhibited superior properties, and the assay demonstrated good performance in terms of sensitivity and selectivity. This work features a novel fabrication of 3D CdS@CF networks that can serve as a general platform for PEC bioanalysis. The methodology reported here is expected to inspire new interest for the fabrication of other 3D nanostructured Cd-chalcogenide (S, Se, Te)@CF networks for wide applications in biomolecular detection and beyond.

A novel core-shell structure Ag2S@CeO2 microspheres were synthesized by growing multi-layer CeO2 onto Ag2S particles. Compared with pure Ag2S, the resultant composite catalyst exhibited highly improved peroxidase-like activity. Influences of pH, temperature, H2O2 concentration and the amount of catalyst on the catalytic activity of Ag2S@CeO2 were investigated. Besides, Ag2S@CeO2 displayed a strong affinity towards H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB). Based on the excellent peroxidase-like activity of Ag2S@CeO2 microspheres, a highly sensitive and selectivity colorimetric method for dopamine detection was developed. The possible catalytic mechanism was also studied using fluorescent probe analysis. It is believed that the efficient biosensor based on the as-prepared Ag2S@CeO2 microspheres can apply for biological analysis and environmental monitoring.

Highly sensitive and specific detection of biomarkers is of great importance for diagnosis and treatment of the related diseases or cancers. We herein developed a robust photoelectrochemical (PEC) immunosensor with enhanced sensitivity and specificity based on evident photocurrent output of the photoanode and significant signal amplification of the biocathode. Prostate specific antigen (PSA, Ag) was used as a target model to exhibit analytical performances of the designed PEC immunosensor. Two kinds of CuInS2 quantum dots (CIS QDs) with different composition were modified on the TiO2 nanotubes (TiO2-NTs) electrode to fabricate the photoanode. Due to the co-sensitization effect of the CIS QDs on TiO2-NTs, an evident photocurrent output was generated at the photoanode. For the biocathode, Au nanoparticles (AuNPs) and polydopamine (PDA) were modified in order on indium-tin oxide (ITO) electrode to immobilize capture PSA antibody (Ab1). Carboxyl-modified polystyrene (PS) nanospheres were coated with secondary antibodies (Ab2) to form PS@Ab2 conjugates, which were used as signal amplifiers via the specific immunoreaction between Ag and Ab2. Based on joint action of evident photocurrent output of the photoanode and significant signal amplification of the biocathode, the designed PEC immunosensor exhibited an ultralow detection limit of 3.4 fg/mL for target PSA detection. Meanwhile, it also showed an enhanced specificity owing to the separation of the photoanode and the biocathode.

Ionic chiral selectors have been received much attention in the field of asymmetric catalysis, chiral recognition, and preparative separation. It has been shown that the addition of ionic chiral selectors can enhance the recognition efficiency dramatically due to the presence of multiple intermolecular interactions, including hydrogen bond, π-π interaction, van der Waals force, electrostatic ion-pairing interaction, and ionic-hydrogen bond. In the initial research stage of the ionic chiral selectors, most of work center on the application in chromatographic separation (capillary electrophoresis, high-performance liquid chromatography, and gas chromatography). Differently, more and more attention has been paid on the spectroscopy (nuclear magnetic resonance, fluorescence, ultraviolet and visible absorption spectrum, and circular dichroism spectrum) and electrochemistry in recent years. In this tutorial review as regards the ionic chiral selectors, we discuss in detail the structural features, properties, and their application in chromatography, spectroscopy, and electrochemistry.

A nanoflare, a conjugate of Au nanoparticles (NPs) and fluorescent nucleic acids, is believed to be a powerful nanoplatform for diagnosis and therapy. However, it highly suffers from the nonspecific detachment of nucleic acids from the AuNP surface because of the poor stability of Au-S linkages, thereby leading to the false-positive signal and serious side effects. To address these challenges, we report the use of covalent amide linkage and functional Au@graphene (AuG) NP to fabricate a covalent conjugate system of DNA and AuG NP, label-rcDNA-AuG. Covalent coating of abundant amino groups (-NH2) onto the graphitic shell of AuG NP efficiently facilitates the coupling with carboxyl-labeled capture DNA sequences through simple, but strong, amide bonds. Importantly, such an amide-bonded nanoflare possesses excellent stability and anti-interference capability against the biological agents (nuclease, DNA, glutathione (GSH), etc.). By accurately monitoring the intracellular miR-21 levels, this covalent nanoflare is able to identify the positive cancer cells even in a mix of cancer and normal cells. Moreover, it allows for efficient photodynamic therapy of the targeted cancer cells with minimized side effects on normal cells. This work provides a facile approach to develop a superstable nanosystem showing promising potential in clinical diagnostics and therapy.

For SERS analysis in living cells, the inevitable desorption of Raman molecule on the substrate surface is a key challenge. To ensure high stability, SERS systems with Raman molecules protected inside the core-Raman molecule-shell (C-M-S) structures have been designed, but at the expense of sacrificed sensing performances. Here a shell-switchable SERS blocking strategy is developed for the reliable SERS analysis in living cells, relying on the shell blockers to regulate the SERS sensing signal without affecting the internal Raman molecules. After several C-M-S structures were investigated, the SERS blocking mechanism confirmed that thick shells (Au, Ag, ZnO, and MnO2) can cause a significant reduction in the internal SERS signal by obstructing the penetration of the laser or signal. The CAu-Mpy-SAu-SMnO2 nanoprobe is designed for the ratiometric SERS sensing in living cells, which retains sensing performances even though the Raman molecule is protected inside the nanostructure. This SERS strategy makes the turn-on sensing achievable in living cells with the MnO2 shell as a signal switch and a Raman reference. Additionally, it allows for accurate monitoring of the degradation of MnO2 carriers in living cells, even without fluorescent labels.

Pathogenic bacterial fouling in agriculture and food-associated products poses mounting food safety concerns today. Efficient integration of precise tracking and on-demand bacterial killing to achieve the source control of pathogenic bacteria at the single-cell level is one of the most valuable antifouling methods for safeguarding food safety but remains unexplored. Here, we report an all-in-one design strategy as a proof of concept to establish a stimuli-responsive nanoprobe PDANSs-FAM-Apt for the detection of Staphylococcus aureus (S. aureus) at the single-cell level, which could be capable of guiding the on-demand photothermal killing of bacteria upon near-infrared (NIR) light irradiation. By examining the size-dependent modulation of the fluorescence resonance energy transfer efficiency to polydopamine nanospheres (PDANSs), PDANSs-FAM-Apt was finally assembled by 6-carboxyfluorescein-terminated S. aureus, binding the aptamer (FAM-Apt) and PDANSs at ∼258 nm through π-π stacking interactions. As a result, PDANSs-FAM-Apt exhibits a remarkable fluorescence enhancement (∼261-fold) to S. aureus with a satisfactory detection limit of 1.0 cfu/mL, allowing for assay at the single-cell level and thus ultralow background fluorescence imaging of S. aureus as well as its biofilms. Moreover, PDANSs-FAM-Apt shows a high photothermal bactericidal property upon NIR light irradiation, endowing it with the strong capacity to efficiently produce heat for destroying S. aureus and its biofilms with the guidance of imaging results. This work emphasizes the versatility of using the combination of stimuli-responsive fluorescence imaging dependent on the PDANS size modulation and NIR light-activated photothermal antibacterial activity to design stimuli-responsive nanoprobes with an improved precision for pathogenic bacteria monitoring and source controlling, which opens a promising antifouling avenue to eliminate bacteria and disrupt bacterial biofilms in agriculture and food-related industries.

Photocathodic bioassays have shown great potential to apply in real bio-sample detection owning to their intrinsic abilities against interference from reductive species. However, the pursuit of photocathodic bioassays with excellent detection performance is still in the infancy. Herein, an advanced signal amplifier of platinum-based nanocatalyst with efficient oxygen reduction capability was explored to build a high-performance photocathodic immunoassay. The target model of carbohydrate antigen 19-9 (CA19-9, Ag) was used for describing the sensing platform. Specifically, the nontoxic Au/CuBi2O4 photocathode was first prepared by decorating Au nanoparticles on CuBi2O4 nanofilm and was used as the matrix to anchor capture CA19-9 antibody (Ab1). Platinum (Pt) nanoparticles were loaded on graphene (GR) nanosheet to form Pt/GR nanocomposite, which was utilized as signal amplifier conjugating with signal CA19-9 antibody (Ab2). When specific sandwich immunoreaction happened, the Pt/GR played the role of an efficient nanocatalyst to accelerate the reduction reaction of electron acceptor of oxygen in the electrolyte, causing evidently enhanced cathodic photocurrent signal. By incorporating this superior signal amplification strategy into the anti-interference photocathodic immunoassay, highly sensitive and specific detection of target Ag was realized. This work pioneers a new perspective for the design of advanced photocathodic bioanalysis for various targets of interest.

Sensitive but with simple, inexpensive detection of disease-related biomarkers in real biological samples is of quite necessity for early diagnosis and disease surveillance. We herein first introduced high-activity Fe3O4 nanozyme as signal amplifier to develop an ultrasensitive photoelectrochemical (PEC) immunoassay, which meanwhile has the distinct merits of both simplicity and low cost compared with previously reported enzyme-labeling PEC immunoassays. In the proposal, to illustrate and describe the PEC platform, prostate-specific antigen (PSA, Ag) was used as a target model. Specifically, ZnO nanorods (ZnO-NRs) grown vertically on a bare indium–tin oxide (ITO) electrode was deposited with ZnIn2S4 nanocrystals, producing ZnIn2S4/ZnO-NRs/ITO photoelectrode as the PEC matrix to modify capture PSA antibody (Ab1). Histidine-modified Fe3O4 (his-Fe3O4) nanozyme as signal amplifier was linked with signal PSA antibody (Ab2) to form his-Fe3O4@Ab2 conjugate, and was anchored through specific sandwich immunoreaction. The labeling his-Fe3O4 nanozyme acted as a peroxidase to induce the generation of the insoluble and insulating precipitation, resulting in an evident decrease in the photocurrent signal. On account of combined effects of high catalytic efficiency of the his-Fe3O4 nanozyme and excellent PEC properties of the ZnIn2S4/ZnO-NRs/ITO photoelectrode, ultralow detection limit of 18 fg/mL for target Ag detection was achieved. Besides, as high-activity his-Fe3O4 nanozyme has substituted natural enzyme as signal amplifier, simplicity and low cost of the PEC immunoassay was realized.

The combination of surface-enhanced Raman scattering (SERS) imaging technology with near-infrared (NIR) light-triggered photothermal therapy is of utmost importance to develop novel theranostic platforms. Herein, an aptamer-conjugated Au nanocage/SiO2 (AuNC/SiO2/Apt) core-shell Raman nanoprobe has been rationally designed as the bifunctional theranostic platform to fulfill this task. In this theranostic system, the Raman-labeled Au nanocage (AuNC) was encapsulated into a bioinert shell of SiO2, followed by conjugating aptamer AS1411 as the target-recognition moiety. AuNC served as the SERS-active and photothermal substrate due to its large free volume, built-in plasmon effect, and NIR photothermal capacity, while the SiO2 coating endowed the nanoprobes with good stability and biocompatibility, as well as abundant anchoring sites for surface functionalization. Considering their prominent SERS and photothermal properties, the application potential of the AuNC/SiO2/Apt nanoprobes was investigated. The proposed nanoprobes could be applied to targeted detection and SERS imaging of nucleolin-overexpressing cancer cells (MCF-7 cells as the model) from normal cells and also exhibited acceptable photothermal efficacy without systematic toxicity. This theranostic nanoplatform provided a possible opportunity for in situ diagnosis and noninvasive treatment of cancer cells by SERS imaging-guided photothermal therapy.

In this study, an electroactive rotaxane, (S,S)-crown-3, consisting of a polymeric chiral ionic liquid as a flexible axle and 18-crown-6 as the wheel, was designed and synthesized. It is worth noting that a stimuli-responsive system was developed, in which the wheel could switch its location between the chiral carbamido group and ionic pair of the ionic polymers under an external force. Next, (S,S)-crown-3 was employed as a modification on the surface of glassy electrode. In contrast to previous study, the developed probe presented a clear discrimination of an electrochemical signal in the absence of Cu(ii). Under the external force (different pH values), l-isomers of amino acids (tryptophan, tyrosine, and cysteine) could form stable host-guest interactions with the chiral carbamido group, producing higher peak currents than the d-isomers. Compared to the absence of the crown, (S,S)-crown-3 showed much better recognition efficiency. The value of IL/ID for tryptophan could reach 39.8. In brief, the present study describes a powerful method for the synthesis of an electroactive rotaxane with great enantiorecognition capability.

5,10,15,20-Tetrakis(4-carboxyl phenyl)porphyrin (Por) modified Co(OH)2 deposited on the surface of GO nanocomposites (Por/Co(OH)2/GO) were prepared and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and XRD. For the first time, H2TCPP/Co(OH)2/GO is found to have enhanced peroxidase-like activity and catalyze the oxidation of the substrate 3,3,5,5-tetramethylbenzidine (TMB) by hydrogen peroxide (H2O2). Notably, the colorless TMB rapidly transformed into blue oxTMB in just 60 s, which was easily observed visually. The catalytic kinetics of H2TCPP/Co(OH)2/GO is in accord with the Michaelis-Menten equation. The catalytic mechanism of H2TCPP/Co(OH)2/GO nanocomposites is attributed to hydroxyl radicals (˙OH), due to decomposition of H2O2, which is verified by using terephthalic acid as a fluorescent probe. What's more, H2O2 can be detected in a wide linear detection range from 5 to 35 mM with a detection limit of 0.385 mM. Furthermore, based on the excellent peroxidase-like activity of H2TCPP/Co(OH)2/GO, a colorimetric sensor is established to sensitively detect glutathione (GSH) in a linear range from 10 to 300 μM with a low detection limit of 9.5 μM.

Low fouling electrochemical immunosensors with both "signal-off" and "signal-on" analytical methods were developed for the highly sensitive and efficient detection of cancer antigen 15-3 (CA 15-3) in human serum samples. The antifouling sensing interfaces were constructed by assembling multifunctional polyethylene glycol on gold electrodes, followed by covalent conjugation with CA 15-3 antibody. Pure antigens and Fe3O4@Ag will competitively bind to the immobilized antibody on the electrode. Fe3O4 magnetic nanoparticles attached to the working electrode and collected by a magnetic electrode were treated via electrochemical conversion to generate electroactive Prussian blue as a signal readout. Therefore, these two signals measured independently were complementary, and this design allowed one to choose the assay method according to real situations so as to ensure accuracy of the immunosensor. Moreover, owing to its good antifouling property, the immunosensor was capable of detecting CA 15-3 even in complex human serum samples, demonstrating potential application in quantitative analysis of real patient serum samples.

Cathode photoelectrochemical immunoassay usually shows better anti-interference capacity toward real samples than anode photoelectrochemical immunoassay. However, its poor photocurrent response has greatly restricted the detection sensitivity. Herein, a promising ultrasensitive cathode photoelectrochemical immunoassay was developed based on TiO2 photoanode-enhanced 3D Cu2O nanowire array (NWA) photocathode, and coupled with signal amplification by horseradish peroxidase (HRP)-induced biocatalytic precipitation (BCP). Carcinoembryonic antigen (CEA, Ag) was used as a detection model, TiO2 nanoparticle-modified indium tin oxide (ITO) electrode served as the photoanode, and Cu2O NWAs grown in situ on Cu mesh was both the photocathode and photoelectrochemical matrix to immobilize the capture CEA antibodies (Ab1). The signal CEA antibodies (Ab2) were labeled with HRP to form Ab2-HRP bioconjugates, and employed as signal amplifiers when the specific immunoreaction occurred. The developed photoanode-enhanced cathode photoelectrochemical immunoassay has good anti-interference capability, outstanding photocurrent response, and high sensitivity for target Ag detection, which was attributed to the synergistic effects of the 3D nanostructure of Cu2O NWA photocathode, the introduction of TiO2 photoanode as counter electrode, and the signal amplification of Ab2-HRP bioconjugate-induced BCP. The developed cathode photoelectrochemical immunoassay showed a low limit of detection (0.037 pg mL−1) with a wide linear range (from 0.1 pg mL−1 to 50 ng mL−1) for CEA detection.

An ultrasensitive photoelectrochemical (PEC) biosensor was developed based on cosensitization of biocompatible CuInS2/ZnS quantum dots (ZCIS QDs) and N-doped carbon dots (N-CDs) coupled with dual c...

Previous work on photoelectrochemical (PEC) biosensors has demonstrated that the photoanode-based type possesses satisfying sensitivity, because photoanode utilize electrons as the majority charge carriers and a distinct photocurrent can be generated when electron donors are furnished. However, as hole-oxidation reaction occurs at the photoanode interface, the photoanode-based PEC sensor has inferior anti-interference capacity to reductive substances coexisting in the biological sample, leading to a challenged selectivity. Herein, a universal design on selectivity-enhanced PEC enzyme sensor was proposed by integrating a photoanode with a biocathode. Specifically, the CuInS2 sensitization layer and ZnS passivation layer were deposited in sequence on the TiO2 film modified indium-tin oxide (ITO) electrode mainly by successive ionic layer adsorption and reaction (SILAR) means, forming the hybrid ZnS/CuInS2/TiO2/ITO photoanode. A carbon fiber paper (CFP) electrode was modified with biocatalysts of enzymes via the assistance of chitosan (CS) to fabricate the biocathode. Utilizing glucose oxidase (GOx) and horserdish peroxidase (HRP) as biocatalysts, a selectivity-enhanced PEC sensor for glucose was developed. The PEC sensing platform integrating photoanode with biocathode not only inherits distinct photocurrent of the photoanode-based sensor but also possesses enhanced selectivity, because just the biocathode was incubated in the biological sample and there is no interaction between the photoanode and coexisting reductive substances.

Sensitive and specific detection of DNA is of great significance for clinical diagnosis. In this paper, an effective cascade signal amplification strategy was introduced into photoelectrochemical (PEC) biosensor for ultrasensitive detection of human T-cell lymphotropic virus type I (HTLV-I) DNA. This proposed signal amplification strategy integrates λ-exonuclease (λ-Exo) aided target recycling with hybridization chain reaction (HCR) and enzyme catalysis. In the presence of target DNA (tDNA) of HTLV-I, the designed hairpin DNA (h1DNA) hybridized with tDNA, subsequently recognized and cleaved by λ-Exo to set free tDNA. With the λ-Exo aided tDNA recycling, an increasing number of DNA fragments (output DNA, oDNA) were released from the digestion of h1DNA. Then, triggered by the hybridization of oDNA with capture DNA (cDNA), numerous biotin-labeled hairpin DNAs (h2DNA and h3DNA) could be loaded onto the photoelectrode via the HCR. Finally, avidin-labeled alkaline phosphatase (avidin-ALP) could be introduced onto the electrode by specific interaction between biotin and avidin. The ALP could catalyze dephosphorylation of phospho-L-ascorbic acid trisodium salt (AAP) to generate an efficient electron donor of ascorbic acid (AA), and thereby greatly increasing the photocurrent signal. By utilizing the proposed cascade signal amplification strategy, the fabricated PEC biosensor exhibited an ultrasensitive and specific detection of HTLV-I DNA down to 11.3 aM, and it also offered an effective strategy to detect other DNAs at ultralow levels.

The ability to rapidly detect apoptotic cells and accurately evaluate therapeutic effects is significant in cancer research. To address this target, a biocompatible, ultrasensitive photoelectrochemical (PEC) cytosensing platform was developed based on electrochemically reduced graphene (EG)/ZnIn2S4 cosensitized TiO2 coupled with specific recognition between apoptotic cells and phosphatidylserine-binding peptide (PSBP). In this strategy, the HL-60 cells were selected as a model and C005, nilotinib, and imatinib were selected as apoptosis inducers to show cytosensing performances. In particular, a TiO2 photoactive substrate was designed as hollow spheres to enhance the PEC performance. Graphene was electrodeposited on the hollow TiO2-modified electrode to accelerate electron transfer and increase conductivity, followed by in situ growth of ZnIn2S4 nanocrystals as photosensitizers via successive ionic layer adsorption and reaction method, forming a TiO2/EG/ZnIn2S4 cosensitized structure that was used as a PE...

A general, efficient strategy for a self-powered PEC immunoassay with an evident photocurrent response was proposed by separating the photoanode from recognition events. The immunoassay demonstrates the exciting features of both high sensitivity and anti-interference capabilities.

Herein, a novel and robust two-electrode photoelectrochemical (PEC) biosensing platform amplified by bilirubin oxidase (BOD) labelling was reported. This two-electrode operating system was composed of photoanode and sensing biocathode. Carcinoembryonic antigen (CEA) was utilized as a model for probing. Specifically, Fe3+-doped TiO2 (Fe:TiO2) nanotubes were first prepared and then deposited with ZnIn2S4 (ZIS) nanocrystals to develop the ZIS/Fe:TiO2 photoanode. Toward sensing biocathode, after carbon nanotubes (CNTs) and Au nanoparticles (NPs) were modified on conductive glass, an Au/CNT cathodic substrate was fabricated to anchor the CEA aptamer. Complementary DNA (cDNA) of the CEA aptamer was labelled with BOD to form the cDNA-BOD conjugate that amplified the signal through DNA hybridization. Target detection hinged on an evident decline in the current signal generated by terminated amplification of the BOD labels and evident steric hindrance of the captured CEA molecules. Profiting from excellent PEC property of the ZIS/Fe:TiO2 photoanode and good oxygen-reduction capability of the BOD labels, the two-electrode PEC biosensing platform exhibited high sensitivity. Because of the division of biorecognition with photoanode, the platform also showed satisfactory selectivity in biological matrix. This elegant two-electrode strategy offers a promising path for seeking other robust PEC biosensors applying in complex biological samples.

Fluoroquinolone antibiotics (FQs), a new class of pollutants that seriously threaten human health through environmental and food residues, have aroused wide public concern. However, little attention has been paid to the potential toxicity of FQs' metal complex. Here, we firstly explore the proof-of-concept study of FQs' metal complex to bind bovine serum albumin (BSA) using systematical spectroscopic approaches. In detail, we have found that the complex of Al3+ with gatifloxacin (Al(III)-GFLX complex) can effectively bind to BSA via electrostatic interaction in PBS buffer (pH = 7.4, 1×), resulting in the formation of Al(III)-GFLX-BSA complex. The negative value of ΔG shows that the binding of Al(III)-GFLX complex to BSA is a spontaneous process. Circular dichroism spectra verify that Al(III)-GFLX complex effectively triggers the conformation changes of BSA's secondary structure. It has been proved that the interaction of small molecule with serum albumin has a significant effect on their in vivo biological effects such as absorption, distribution, metabolism, and excretion, and etc. Therefore, the results of this paper may offer a valuable theoretical basis for establishing safety standards of FQs' metal complex to ensure food and environmental health.