Photoelectrochemical detection of pentachlorophenol with a Multiple Hybrid CdSexTe1−x/TiO2 Nanotube Structure-Based Label-Free Immunosensor

High-Performance Photocatalytic Multifunctional Material Based on Bi4Ti3O12-Supported Ag and Ti3C2Tx for Organic Degradation and Antibacterial Applications

With the rapid development of modern science and technology and the diversification of social needs, traditional single-performance materials struggle to meet the complex and changeable application scenarios. To address the multifaceted requirements of biomedical applications, such as disease diagnosis and treatment, scientists are dedicated to developing new multifunctional biomaterials with multiple activities. Bi4Ti3O12 (BTO), despite its versatility and application potential, has insufficient photocatalytic performance. Silver nanoparticles (Ag) and Ti3C2Tx are particularly effective as antibacterial materials but they have relatively single functions. In this study, BTO/Ag/Ti3C2Tx biomultifunctional materials were constructed by combining BTO with Ag and Ti3C2Tx. We discovered that the addition of Ag and Ti3C2Tx effectively optimized the visible light absorption characteristics of BTO, reduced the electron transfer resistance, and increased the carrier concentration, thus significantly improving the photocatalytic performance of composite material, thereby markedly improving the composite's photocatalytic performance and its efficacy in photochemical sensing and photodegradation. At the same time, BTO, as a carrier, effectively avoids Ag and Ti3C2Tx agglomeration and gives full play to its antibacterial properties. In the specific performance studies, ascorbic acid and MB were used as the subjects of photochemical sensing and photodegradation properties, while Escherichia coli and Staphylococcus aureus were tested for antibacterial properties. The BTO/Ag/Ti3C2Tx composite showed remarkable results in all assessments, demonstrating its potential as a versatile antibacterial and photocatalytic material.

Photoelectrochemical immunoassay of cardiac troponin I based on ZnTCPP/CdIn2S4 type-II heterojunction and co-catalyzed precipitation biolabeling

CdIn2S4 and zinc tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP) were synthesized by hydrothermal method, and an organic dye-sensitized inorganic semiconductor ZnTCPP/CdIn2S4 type II heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode. A sandwich immunostructure for signal-attenuation photoelectrochemical (PEC) detection of cardiac troponin I (cTnI) was constructed using the ZnTCPP/CdIn2S4/FTO photoanode and a horseradish peroxidase (HRP)-ZnFe2O4-Ab2-bovine serum albumin (BSA) immunolabeling complex. The bioenzyme HRP and the HRP-like nanozyme ZnFe2O4 can co-catalyze the oxidation of 4-chloro-1-naphthol (4-CN) by H2O2 to produce an insoluble precipitate on the photoanode, thus notably reducing the anodic photocurrent for quantitative determination of cTnI. Under the optimal conditions, the photocurrent at 0 V vs. SCE in 0.1 M phosphate buffer solution (pH 7.40) containing 0.1 M ascorbic acid was linear with the logarithm of cTnI concentration from 500 fg mL-1 to 50.0 ng mL-1, and the limit of detection (LOD, S/N = 3) is 0.15 pg mL-1. Spiked recoveries were 95.1% ~ 104% for assay of cTnI in human serum samples.

Flow injection analysis coupled with photoelectrochemical immunoassay for simultaneous detection of anti-SARS-CoV-2-spike and anti-SARS-CoV-2-nucleocapsid antibodies in serum samples

A thin-layer flow cell of low internal volume (12 μL) is incorporated in a flow injection analysis (FIA) system for simultaneous and real-time photoelectrochemical (PEC) immunoassay of anti-SARS-CoV-2 spike 1 (S1) and anti-SARS-CoV-2 nucleocapsid (N) antibodies. Covalent linkage of S1 and N proteins to two separate polyethylene glycol (PEG)-covered gold nanoparticles (AuNPs)/TiO2 nanotube array (NTA) electrodes affords 10 consecutive analyses with surface regenerations in between. An indium tin oxide (ITO) allows visible light to impinge onto the two electrodes. The detection limits for anti-S1 and anti-N antibodies were estimated to be 177 and 97 ng mL-1, respectively. Such values compare well with those achieved with other reported methods and satisfy the requirement for screening convalescent patients with low antibody levels. Additionally, our method exhibits excellent intra-batch (RSD = 1.3%), inter-batch (RSD = 3.4%), intra-day (RSD = 1.0%), and inter-day (RSD = 1.6%) reproducibility. The obviation of an enzyme label and continuous analysis markedly decreased the assay cost and duration, rendering this method cost-effective. The excellent anti-fouling property of PEG enables accuracy validation by comparing our PEC immunoassays of patient sera to those of ELISA. In addition, the simultaneous detection of two antibodies holds great potential in disease diagnosis and immunity studies.

Universal Hydrogen-Treated TiO2 Nanorod Array/Ti2COX MXene PEC Aptamer Sensor Modulated by the Transport Characteristic of Photogenerated Holes

A semiconductor photoelectrochemical (PEC) aptamer sensor has been widely researched in recent years because of its broad application prospects. However, a universal PEC sensor has not been achieved, and its sensing mechanism based on a photogenerated carrier transfer process has yet to be elucidated. Herein, a novel hydrogen-treated TiO₂ nanorod array one-dimensional (1D)/Ti₂CO_X MXene two-dimensional (2D) (H-TiO₂/Ti₂CO_X) PEC aptamer sensor is presented, which achieved a record detection range of 10^-9-10³ μg/L and a limit of detection (LOD) of 1 fg/L for microcystic toxins-LR detection. Besides, the PEC sensor can also test serotonin (5-HT), aflatoxin-B1, and prostate-specific antigen (PSA) with high performance by changing the aptamers, exhibiting favorable application universality. Furthermore, a new phenomenon of a switchable enhanced/suppressed photocurrent detection signal was discovered from H-TiO₂/Ti₂CO_X PEC aptamer sensors through the variation of the length of the TiO₂ nanorod. Meanwhile, it reveals that the steric hindrance effect determines the photogenerated hole transfer and depolarization processes, which is proposed for the first time as the predominant mechanism of the switchable enhanced/suppressed photocurrent signal for PEC sensors, giving possibilities to develop PEC sensors with higher efficiency.

A near-infrared light-driven photoelectrochemical aptasensing platform for adenosine triphosphate detection based on Yb-doped Bi2S3 nanorods

Due to its capability of low spectral interference, high light stability, and minimal photodamage to biological species, near-infrared (NIR) light is advantageous in biosensing and biochemical analysis. This work developed a photoelectrochemical (PEC) aptasensor for adenosine triphosphate (ATP) detection using NIR light as the irradiation source. In order to utilize NIR light, we prepared Yb-doped Bi₂S₃ (Yb-Bi₂S₃) nanorods to act as photoelectric transducing materials. Due to the unfilled 4f orbitals of Yb which introduced the impurity level between the valence band and conduction band of Bi₂S₃, Yb-Bi₂S₃ exhibited admirable photo-to-current conversion efficiency under NIR light irradiation. The Yb-Bi₂S₃ modified electrode was employed to construct a NIR light-driven PEC sensor using an ATP-binding aptamer as the recognition element. When ATP was present, the photocurrent signal of the proposed aptasensor declined, owing to the formation of an ATP-aptamer complex which enhanced the steric hindrance of electron transfer on the electrode. Under optimal conditions, the sensor showed a sensitive response to ATP in the concentration range from 0.5 to 300 nmol L^-1 with a detection limit of 0.1 nmol L^-1. The proposed aptasensor exhibited high selectivity, good repeatability and desirable stability. Moreover, it was successfully applied to ATP detection in human serum samples.

Selective and sensitive photoelectrochemical aptasensor for streptomycin detection based on Bi4VO8Br/Ti3C2 nanohybrids

Sensitive detection of streptomycin (STR) has attracted increasing attention worldwide because of the relationship between food security and human health. In this paper, Bi₄VO₈Br/Ti₃C₂ nanohybrids were obtained by one-pot solvent hydrothermal method. It was modified on ITO electrode, and STR aptamer was acted as the recognition element. With excellent photoelectrochemical (PEC) performance of Bi₄VO₈Br/Ti₃C₂ nanohybrids, an "on-off-on" PEC aptasensor for STR detection was effectively developed. Compared with pure Bi₄VO₈Br, the photocurrent intensity of as-prepared Bi₄VO₈Br/Ti₃C₂ nanohybrids was about 9 times higher, which ascribed to the highly conductive of Ti₃C₂, driving the photogenerated electrons transferred to the ITO electrode rapidly, so that the recombination of photogenerated electron and hole pairs was inhibited viably. Furthermore, the constructed "on-off-on" PEC aptasensor accomplished STR detection with high sensitivity, excellent specificity and distinguished repeatability in honey. The photocurrent increased with the increment of STR concentration with the linear range from1 nM to 1000 nM, and the detection limit of 0.3 nM (S/N = 3). Compared with the national standard method (SN/T 1925-2007), the as-constructed PEC sensor showed the consistent results.

A metal-free and preconcentration-free method for non-enzymatic amperometric determination of pentachlorophenol using a ZIF-derived hollow carbon material

An enzyme-free, metal-free, and preconcentration-free electrochemical sensor for pentachlorophenol assay has been fabricated. The interface of the sensor is based on a hollow zeolitic imidazolate framework-derived mesoporous carbon material (denoted as HZC/SPCE). The sensor exhibits linear amperometric response upon pentachlorophenol at 0.82 V (vs. Ag/AgCl) in the concentration range 0.001 to 26.8 mg L^-1 (3.75 × 10^-8~1.006 × 10^-4 M) (R² = 0.997). The sensitivity of HZC/SPCE is 3.53 × 10² μA mM^-1 cm^-2 with a detection limit of 2.05 × 10^-9 M (S/N = 3) for pentachlorophenol. The method has been applied to the determination of pentachlorophenol in spiked food packaging samples with recoveries in the range 92.0 to 107.0%. Graphical abstract Schematic representation of the synthesis of hollow ZIFs-derived hollow carbon material. Free protons derived from tannic acid penetrated into ZIF-8 to destroy its solid framework and the outer parts covered by tannic acid were protected from further etching. After pyrolysis, the morphology of HZC remained similar to that of HZIF-8. Abbreviation: CTAB: hexadecyl trimethyl ammonium bromide; Melm: 2-methylimidazole; ZIF-8: zeolitic imidazolate framework-8; TA: tannic acid; HZIF-8: hollow zeolitic imidazolate framework-8; HZC: hollow zeolitic imidazolate frameworks (ZIFs)-derived mesoporous carbon material.

Femtomolar sensing of Alzheimer's tau proteins by water oxidation-coupled photoelectrochemical platform

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. A key pathogenic event of AD is the formation of intracellular neurofibrillary tangles that are mainly composed of tau proteins. Here, we report on ultrasensitive detection of total tau (t-tau) proteins using an artificial electron donor-free, BiVO₄-based photoelectrochemical (PEC) analysis. The platform was constructed by incorporating molybdenum (Mo) dopant and iron oxyhydroxide (FeOOH) ad-layer into the BiVO₄ photoelectrode and employing a signal amplifier formed by horseradish peroxidase (HRP)-triggered oxidation of 3,3'-diaminobenzidine (DAB). Despite the absence of additional electron suppliers, the FeOOH/Mo:BiVO₄ conjugated with the Tau5 antibody produced strong current signals at 0 V (vs. Ag/AgCl, 3 M NaCl) under the illumination of a white light-emitting diode. The Mo extrinsic dopants increased the charge carrier density of BiVO₄-Tau5 by 1.57 times, and the FeOOH co-catalyst promoted the interfacial water oxidation reaction of Mo:BiVO₄-Tau5 by suppressing charge recombination. The introduction of HRP-labeled Tau46 capture antibodies to the FeOOH/Mo:BiVO₄-Tau5 platform produced insoluble precipitation on the transducer by accelerating the oxidation of DAB, which amplified the photocurrent signal of FeOOH/Mo:BiVO₄-Tau5 by 2.07-fold. Consequently, the water oxidation-coupled, FeOOH/Mo:BiVO₄-based PEC sensing platform accurately and selectively recognized t-tau proteins down to femtomolar concentrations; the limit of detection and limit of quantification were determined to be 1.59 fM and 4.11 fM, respectively.

Polydopamine-PEG-Folic Acid Conjugate Film Engineered TiO2 Nanotube Arrays for Photoelectrochemical Sensing of Folate Binding Protein

Serum-soluble folate binding protein (FBP) is an important tumor marker, and the development of a simple biosensing method is highly needed. In this work, a photoelectrochemical (PEC) biosensor for the detection of FBP was proposed based on the construction of an antifouling interface and the unique ligand-protein recognition. The PEC sensing platform was prepared by the biomimetic polydopamine (PDA) coating on TiO₂ nanotubes arrays (NTAs). A significant PEC enhancement effect was obtained due to the macroporous structures. Excellent antifouling performance was achieved by conjugation of amino-group-terminated 8-arm poly(ethylene glycol) (PEG). The incorporation of folic acid (FA) retains the antifouling property and shows recognition abilities toward FBP. The fabricated PEC biosensor shows good analytical performance. The combination of ligand-protein recognition and a PEC antifouling interface provides a good consideration for the development of FBP biosensors.

A photoelectrochemical aptasensor based on p-n heterojunction CdS-Cu2O nanorod arrays with enhanced photocurrent for the detection of prostate-specific antigen

A sensitive photoelectrochemical (PEC) aptasensor was constructed for prostate-specific antigen (PSA) detection using an enhanced photocurrent response strategy. The p-n heterostructure CdS-Cu₂O nanorod arrays were prepared on Ti mesh (CdS-Cu₂O NAs/TM) by a simple hydrothermal method and successive ionic-layer adsorption reactions. Compared with the original CdS/TM, the synergistic effect of p-n type CdS-Cu₂O NAs/TM and the internal electric field realizes the effective separation of photoinduced electron-hole pairs and improves the PEC performance. In order to construct the aptasensor, an amino-modified aptamer was immobilized on CdS-Cu₂O NAs/TM to serve as a recognition unit for PSA. After the introduction of PSA, PSA was specifically captured by the aptamer on the PEC aptasensor, which can be oxidized by photogenerated holes to prevent electron-hole recombination and increase photocurrent. Under optimal conditions, the constructed PEC aptasensor has a linear range of 0.1-100 ng·mL^-1 and a detection limit as low as 0.026 ng·mL^-1. The results of aptasensor detection of human serum indicate that it has broad application prospects in biosensors and photoelectrochemical analysis.

Enhanced photoelectrochemical biosensing performance for Au nanoparticle–polyaniline–TiO2 heterojunction composites

A new photoelectrochemical (PEC) sensing platform comprising TiO₂ nanotube arrays (TiONTAs), polyaniline (PANI), and gold nanoparticles (AuNPs) was successfully fabricated. After loading the enzyme, this Au–PANI–TiONTA electrode showed excellent response to glucose at a linear range of 2–36 mM with a 0.02 mM detection limit. Good PEC performance was obtained due to the following advantages of the material: high visible-light harvesting ability for excellent light trapping capacity of PANI and AuNPs, good separation of the photo-induced charges related to the specific Au–PANI–TiONTA heterostructure, efficient electrode surface reaction kinetics derived from the large specific surface area of TiONTAs and improved electrode catalytic activity. This work proposed a new and general PEC enzymatic format and can be extended to prepare different PEC biosensors for biomolecules such as DNA, proteins and substrates of oxidases.

A novel photoelectrode for glucose PEC biosensing composed of TiONTAs, PANI, and AuNPs was successfully obtained. The GOx@Au–PANI–TiONTA electrode exhibited a wide response range (2–36 mM) with a low detection limit (0.02 mM) and good stability.

A photoelectrochemical immunosensor based on CdS/CdTe-cosensitized SnO2 as a platform for the ultrasensitive detection of amyloid β-protein

An ultrasensitive label-free photoelectrochemical immunosensor was developed to detect amyloid β-protein based on CdS/CdTe-cosensitized SnO₂ nanoflowers.

A visible-light-active CuInSe2:Zn/g-C3N4/TiO2 nanowires for photoelectrocatalytic bactericidal effects

A visible-light-active CuInSe₂:Zn/g-C₃N₄/TiO₂ nanowire (NW) photoelectrode was prepared by in situ growth of g-C₃N₄ on the surface of TiO₂ NWs, followed by drop deposition of Zn-doped CuInSe₂ quantum dots (CuInSe₂:Zn QDs).

Gold Nanoparticle-Induced Photocurrent Quenching and Recovery of Polymer Dots: Toward Signal-On Energy-Transfer-Based Photocathodic Bioanalysis of Telomerase Activity in Cell Extracts

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.

Manganese doped CdS sensitized graphene/Cu2MoS4 composite for the photoelectrochemical immunoassay of cardiac troponin I

As a newly emerged photoactive material, Cu₂MoS₄ has motivated wide research interests in the field of photoelectrochemistry. Based on manganese doped CdS (CdS:Mn) sensitized graphene (G)/Cu₂MoS₄ composite, we developed a label-free photoelectrochemical (PEC) immunosensor for the detection of cardiac troponin I (cTnI). G as an excellent 2D conductive material, combined with Cu₂MoS₄ could improve its charge transfer efficiency. CdS:Mn nanoparticles (NPs) loaded on G/Cu₂MoS₄ further enlarged the light absorption range of Cu₂MoS₄ and restrained the electron-hole pairs recombination. Under optimal conditions, the proposed PEC immunosensor responded sensitively to cTnI with a low detection limit of 0.18 pg/mL and a wide linear range (0.005-1000 ng/mL). Moreover, as-fabricated immunosensor also exhibited high sensitivity, excellent selectivity and good stability. This work also was extended to real samples analysis and obtained satisfied results.

A sensitive photoelectrochemical assay of miRNA-155 based on a CdSe QDs//NPC-ZnO polyhedra photocurrent-direction switching system and target-triggered strand displacement amplification strategy

A new photoelectrochemical biosensor based on a CdSe QD//NPC-ZnO polyhedra photocurrent-direction switching system and a target-triggered strand displacement amplification strategy was developed for the detection of miRNA-155.

Organic Photo-Electrochemical Transistor-Based Biosensor: A Proof-of-Concept Study toward Highly Sensitive DNA Detection

Organic bioelectronics have shown promising applications for various sensing purposes due to their significant advantages in term of high flexibility, portability, easy fabrication, and biocompatibility. Here, a new type of organic device, organic photo-electrochemical transistor (OPECT), is reported, which is the combination of an organic electrochemical transistor and a photo-electrochemical gate electrode modified with CdS quantum dots (QDs). Thanks to the inherent amplification function of the transistor, the OPECT-based biosensor exhibits much higher sensitivity than that of a traditional biosensor. The sensing mechanism of the OPECT is attributed to the charge transfer between the photosensitive semiconductor CdS QDs and the gate electrode. In an OPECT-based DNA sensor, target DNA is labeled with Au nanoparticles (NPs) and captured on the gate electrode, which can influence the charge transfer on the gate caused by the exciton-plasmon interactions between CdS QDs and Au NPs. Consequently, a highly sensitive and selective DNA sensor with a detection limit of around 1 × 10^-15 m is realized. It is expected that OPECTs can be developed as a high-performance platform for numerous biological detections in the future.

Gold Nanoparticle Couples with Entropy-Driven Toehold-Mediated DNA Strand Displacement Reaction on Magnetic Beads: Toward Ultrasensitive Energy-Transfer-Based Photoelectrochemical Detection of miRNA-141 in Real Blood Sample

Highly stable circulating microRNAs (miRNAs) are currently recognized as a novel potential biomarker for clinical cancer diagnosis in the early stage. However, limited by its low concentration, high sequence similarity, as well as the numerous interferences in body fluids, detection of miRNA in whole blood with sufficient selectivity and sensitivity is still challenging. Herein, we reported the integration of entropy-driven toehold-mediated DNA strand displacement (ETSD) reaction with magnetic beads (MB) toward the energy-transfer-based photoelectrochemical (PEC) detection of the prostate carcinoma (PCa) biomarker miRNA-141 in a real blood sample. In this protocol, the ETSD reaction was divided into two steps, and cooperated with magnetic separation, target extraction and amplification could be realized in a single test and ultrasensitive detection of miRNA-141 could be achieved in undiluted whole blood sample. This work proposed a new solution for sensitive biomolecular detection in a complex biological milieu and exhibited great promise for future clinical cancer diagnosis.

A versatile cathodic "signal-on" photoelectrochemical platform based on a dual-signal amplification strategy

Novel cathodic photoelectrochemical (PEC) aptasensors for sensitive and selective determination of thrombin and Pb²⁺ were developed based on a new dual-signal amplification strategy. The presence of gold nanoparticles (AuNPs) could quench the PEC signal of bismuth oxyiodide (BiOI). At the same time, the redox moiety G-quadruplex/hemin or ferrocene (Fc) was found to enhance the PEC signal of BiOI. So, in the presence of thrombin or Pb²⁺, the interaction between target and the aptamer resulted in the releasement of the AuNPs, as well as shorter distance between the redox moiety and the electrode surface. Hence dual-enhanced cathodic PEC biosensor strategy was realized. Under the optimized conditions, the detection limits of thrombin and Pb²⁺ were 17.3 fM and 3.16 pM, respectively with good selectivity. At the same time, the PEC performance of redox moiety G-quadruplex/hemin and Fc was compared.

Bismuth Oxyiodide Couples with Glucose Oxidase: A Special Synergized Dual-Catalysis Mechanism for Photoelectrochemical Enzymatic Bioanalysis

On the basis of a special synergized dual-catalysis mechanism, this work reports the preparation of a BiOI-based heterojunction and its use for cathodic photoelectrochemical (PEC) oxidase biosensing, which, unexpectedly, revealed that hydrogen peroxide (H₂O₂) had a greater impact than dioxygen (O₂). Specifically, the BiOI layer was in situ formed on the substrate through an impregnating hydroxylation method for the following coupling with the model enzyme of glucose oxidases (GOx). The constructed cathodic PEC enzyme sensor exhibited a good analytical performance of rapid response, high stability, and good selectivity. Especially, glucose-induced H₂O₂-controlled enhancement of the photocurrent was recorded rather than the commonly observed O₂-dependent suppression of the signal. This interesting phenomenon was attributed to a special synergized dual-catalysis mechanism. Briefly, this study is expected to provide a new BiOI-based photocathode for general PEC bioanalysis development and to inspire more interest in the design and construction of a novel heterojunction for advanced photocathodic bioanalysis. More importantly, the mechanism revealed here would offer a totally different perspective for the use of a biomimetic catalyst in the design of future PEC enzymatic sensing and the understanding of relevant signaling routes as well as the implementation of innovative PEC devices.

Reduced graphene oxide/BiFeO3 nanohybrids-based signal-on photoelectrochemical sensing system for prostate-specific antigen detection coupling with magnetic microfluidic device

A novel magnetic controlled photoelectrochemical (PEC) sensing system was designed for sensitive detection of prostate-specific antigen (PSA) using reduced graphene oxide-functionalized BiFeO₃ (rGO-BiFeO₃) as the photoactive material and target-triggered hybridization chain reaction (HCR) for signal amplification. Remarkably enhanced PEC performance could be obtained by using rGO-BiFeO₃ as the photoelectrode material due to its accelerated charge transfer and improved the visible light absorption. Additionally, efficient and simple operation could be achieved by introducing magnetic controlled flow-through device. The assay mainly involved in anchor DNA-conjugated magnetic bead (MB-aDNA), PSA aptamer/trigger DNA (Apt-tDNA) and two glucose oxidase-labeled hairpins (H1-GOx and H2-GOx). Upon addition of target PSA, the analyte initially reacted with the aptamer to release the trigger DNA, which partially hybridized with the anchor DNA on the MB. Thereafter, the unpaired trigger DNA on the MB opened the hairpin DNA structures in sequence and propagated a chain reaction of hybridization events between two alternating hairpins to form a long nicked double-helix with numerous GOx enzymes on it. Subsequently, the enzymatic product (H₂O₂) generated and consumed the photo-excited electrons from rGO-BiFeO₃ under visible light irradiation to enhance the photocurrent. Under optimal conditions, the magnetic controlled PEC sensing system exhibited good photocurrent responses toward target PSA within the linear range of 0.001 - 100ng/mL with a detection limit of 0.31pg/mL. Moreover, favorable selectivity, good stability and satisfactory accuracy were obtained. The excellent analytical performance suggested that the rGO-BiFeO₃-based PEC sensing platform could be a promising tool for sensitive, efficient and low cost detection of PSA in disease diagnostics.

Visible-light driven Photoelectrochemical Immunosensor Based on SnS2@mpg-C3N4 for Detection of Prostate Specific Antigen

Herein, a novel label-free photoelectrochemical (PEC) immunosensor based on SnS2@mpg-C3N4 nanocomposite is fabricated for the detection of prostate specific antigen (PSA) in human serum. Firstly, mesoporous graphite-like carbon nitride (mpg-C3N4) with carboxyl groups is synthesized successfully which possesses high specific surface area and large pore volume. Then, SnS2 as a typical n-type semiconductor with weak photoelectric conversion capability is successfully loaded on carboxylated mpg-C3N4 to form a well-matched overlapping band-structure. The as-synthesized SnS2@mpg-C3N4 nanocomposite performs outstanding photocurrent response under visible-light irradiation due to low recombination rate of photoexcited electron-hole pairs, which is transcend than pure SnS2 or pure mpg-C3N4. It is worth noting that SnS2@mpg-C3N4 nanocomposite is firstly employed as the photoactive material in PEC immunosensor area. The concentration of PSA can be analyzed by the decrease in photocurrent resulted from increased steric hindrance of the immunocomplex. Under the optimal conditions, the developed PEC immunosensor displays a liner photocurrent response in the range of 50 fg·mL-1 ~ 10 ng·mL-1 with a low detection limit of 21 fg·mL-1. Furthermore, the fabricated immunosensor with satisfactory stability, reproducibility and selectivity provides a novel method for PSA determination in real sample analysis.

AgBr nanoparticles/3D nitrogen-doped graphene hydrogel for fabricating all-solid-state luminol-electrochemiluminescence Escherichia coli aptasensors

It is necessary to develop rapid, simple and accurate detection method for Escherichia coli (E. coli) due to its widely distributed pathogenic bacteria. Herein, we prepared AgBr nanoparticles (NPs) anchored 3D nitrogen-doped graphene hydrogel (3DNGH) nanocomposites with an exceptionally large accessible surface by a simple hydrothermal approach. The as-prepared 3DNGH porous nanocomposite not only showed better conductivity than that of 3D graphene due to introducing nitrogen element into graphene framework, but also provided a high loading volume for immobilizing luminol. Meanwhile the anchored AgBr NPs served as the catalyst can effectively enhance the ECL behavior of luminol. And the resulting luminol/AgBr/3DNGH exhibited more excellent ECL performances, which was about 2, 3, 8 times enhanced respectively, comparing to luminol/AgBr/3DGH, luminol/3DNGH and luminol/AgBr/2DNG. Further, the multifunctional nanoarchitecture was used as the all-solid-state ECL platform for fabricating Escherichia coli aptasensors via glutaraldehyde as crosslinking agent between amine-functionalized E. coli aptamer and luminol/AgBr/3DNGH. Based on the steric hindrance mechanism that E.coli can significantly decrease the ECL intensity, the proposed aptasensor displayed a linear response for E.coli in the range from 0.5 to 500 cfu/mL with an extremely low detection limit of 0.17 cfu/mL (S/N). In addition, this ECL aptasensor possessed great advantages including the simple operation process, low-cost and sensitivity, which provided a promising approach for the E.coli detection in biomedical, food detection and environmental analysis.

Photoelectrochemical immunosensor for methylated RNA detection based on g-C3N4/CdS quantum dots heterojunction and Phos-tag-biotin

N⁶-methyladenosine (m⁶A) is an enigmatic and abundant internal modification in eukaryotic messenger RNA (mRNA), which could affect various aspects of RNA metabolism and mRNA translation. Herein, a novel photoelectrochemical (PEC) immunosensor was constructed for m⁶A detection based on the inhibition of Cu²⁺ to the photoactivity of g-C₃N₄/CdS quantum dots (g-C₃N₄/CdS) heterojunction, where g-C₃N₄/CdS heterojunction was used as photoactive material, anti-m⁶A antibody as recognition unit for m⁶A-containing RNA, Phos-tag-biotin as link unit and avidin functionalized CuO as PEC signal indicator. When CuO was captured on electrode through biotin-avidin affinity reaction and then treated with HCl, Cu²⁺ could be released and Cu_xS would be formed based on the selective interaction between CdS and Cu²⁺, leading the photocurrent obviously decreased. Under the optimal detection conditions, the PEC biosensor displayed a linear range of 0.01-10nM and a low detection limit of 3.53 pM for methylated RNA determination. Furthermore, the developed method could also be used to detect the expression level of m⁶A methylated RNA in serum samples of breast cancer patient before and after operative treatment. The proposed assay strategy has a great potential for detecting the expression methylation level of RNA in real sample.

Bifunctional polydopamine thin film coated zinc oxide nanorods for label-free photoelectrochemical immunoassay

Photoelectrochemical (PEC) detection is a promising method for label-free immunoassay by reporting the specific biological recognition events with electrical signals. However, it is challenging to rationally incorporate immunosensing components with a photocurrent conversion interface, which generally necessitates multistep fabrication and careful tailoring of various components such as photoactive material and biological probe. For high detection reliability and reproducibility, it is highly desirable to rationally construct an efficient PEC interface with architecture as simple as possible. In this work, a novel yet simple PEC immunosensor based on bio-inspired polydopamine (PDA) thin film-coated zinc oxide (ZnO) nanorods was reported. In this PEC immunosensor, the PDA thin film serves simultaneously as a unique sensitizer for charge separation as well as a functional layer for probe antibody attachment. The photocurrent on this electrode under illumination decreases upon the immunoreaction on the surface, possibly due to the blocking effect of formed immunocomplexes on the access of reducing reagent to the photoelectrode, thus offering a simple and reliable platform for PEC label-free immunoassay. By using an antibody-antigen pair as a model, successful label-free immunoassay was achieved with a detection limit of 10pgmL^-1 and a dynamic range from 100pgmL^-1 to 500ngmL^-1. This work demonstrates intriguing electro-optical property and bioconjugation activity of PDA film and may pave the way toward advanced PEC immunoassays.

How cutting-edge technologies impact the design of electrochemical (bio)sensors for environmental analysis. A review

Through the years, scientists have developed cutting-edge technologies to make (bio)sensors more convenient for environmental analytical purposes. Technological advancements in the fields of material science, rational design, microfluidics, and sensor printing, have radically shaped biosensor technology, which is even more evident in the continuous development of sensing systems for the monitoring of hazardous chemicals. These efforts will be crucial in solving some of the problems constraining biosensors to reach real environmental applications, such as continuous analyses in field by means of multi-analyte portable devices. This review (with 203 refs.) covers the progress between 2010 and 2015 in the field of technologies enabling biosensor applications in environmental analysis, including i) printing technology, ii) nanomaterial technology, iii) nanomotors, iv) biomimetic design, and (v) microfluidics. Next section describes futuristic cutting-edge technologies that are gaining momentum in recent years, which furnish highly innovative aspects to biosensing devices.

Determination of pentachlorophenol by anodic electrochemiluminescence of Ru(bpy)32+ based on nitrogen-doped graphene quantum dots as co-reactant

A novel ultrasensitive Ru(bpy)₃²⁺-based anodic ECL sensor using NGQDs as co-reactant was developed for PCP detection.