Tailoring heterostructured Bi2MoO6/Bi2S3 nanobelts for highly selective photoelectrochemical analysis of gallic acid at drug level

One-pot solvothermal synthesis of Bi/Bi2S3/Bi2WO6 S-scheme heterojunction with enhanced photoactivity towards antibiotic oxytetracycline degradation under visible light

A novel noble-metal-free ternary Bi/Bi₂S₃/Bi₂WO₆ S-scheme heterojunction and Schottky junction was successfully synthesized by one-pot solvothermal method. UV-Vis spectroscopy showed improved light absorption in the ternary composite structure. Electrochemical impedance spectroscopy and photoluminescence spectroscopy confirmed the reduced interfacial resistivity and photogenerated charge recombination rate of the composites. Using oxytetracycline (OTC) as model pollutant, Bi/Bi₂S₃/Bi₂WO₆ presented high photocatalytic activity towards OTC degradation, where the removal rate of Bi/Bi₂S₃/Bi₂WO₆ was 1.3 and 4.1 times higher than that of Bi₂WO₆ and Bi₂S₃ under visible light irradiation in 15 min, respectively. The excellent visible photocatalysis activity was attributed to the SPR effect of metal Bi and the direct S-scheme heterojunction of Bi₂S₃ and Bi₂WO₆ with the matched energy band structure, which led to the increased electron transfer rate and high separation efficiency of the photogenerated election-hole pairs. After seven cycles, the degradation efficiency for 30 ppm OTC with Bi/Bi₂S₃/Bi₂WO₆ only decreased 20.4%. In the degradation solution, the composite photocatalyst leached only 16 ng/L Bi and 26 ng/L W of metal with high photocatalytic stability. Moreover, free radical quenching experiment and electron spin-resonance spectroscopy experiment revealed that ·O₂^-, ¹O₂, h⁺ and ·OH played crucial roles in the photocatalytic degradation of OTC. Based on the analysis of high performance liquid chromatography-mass spectrometry for the intermediates in the degradation process, the degradation pathway was provided. Finally, combined with ecotoxicological effect analysis, the decreased toxicity of OTC after degradation towards rice seedlings was confirmed.

A Recognition-Molecule-Free Photoelectrochemical Sensor Based on Ti3C2/TiO2 Heterostructure for Monitoring of Dopamine

Herein, a novel, recognition-molecule-free electrode based on Ti₃C₂/TiO₂ composites was synthesized using Ti₃C₂ as the Ti source and TiO₂ in situ formed by oxidation on the Ti₃C₂ surface for the selective detection of dopamine (DA). The TiO₂ in situ formed by oxidation on the Ti₃C₂ surface not only increased the catalytically active surface for DA binding but also accelerated the carrier transfer due to the coupling between TiO₂ and Ti₃C₂, resulting in a better photoelectric response than pure TiO₂. Through a series of experimental conditions optimization, the photocurrent signals obtained by the MT100 electrode were proportional to the DA concentration from 0.125 to 400 µM, with a detection limit estimated at 0.045 µM. We also monitored DA in human blood serum samples using the MT100 electrode. The results showed good recovery, demonstrating the promising use of the sensor for the analysis of DA in real samples.

A non-enzymatic photoelectrochemical sensor based on g-C3N4@CNT heterojunction for sensitive detection of antioxidant gallic acid in food

Gallic acid (GA) is found in a wide range of natural plants and is relevant to the health of human beings. Here, a photoelectrochemical sensing platform based on g-C₃N₄@CNT heterojunction has been prepared for the highly sensitive and selective detection of GA. Under the light of xenon lamp, the photocurrent of g-C₃N₄@CNT is 7 times higher than that of g-C₃N₄. And the sensor generates 4 times more photocurrent in the presence of GA than without GA. This sensor has a wide linear range from 10 nM to 10 μM with a limit of detection as low as 2 nM. Also, the abundant amino groups of g-C₃N₄ provide excellent selectivity for the sensor. Furthermore, the sensor can be used for the analysis of GA in black tea samples, which provides a novel and rapid method for the detection of GA in food samples.

In Situ Formation of Bi2MoO6-Bi2S3 Heterostructure: A Proof-Of-Concept Study for Photoelectrochemical Bioassay of l-Cysteine

A novel signal-increased photoelectrochemical (PEC) biosensor for l-cysteine (L-Cys) was proposed based on the Bi₂MoO₆–Bi₂S₃ heterostructure formed in situ on the indium–tin oxide (ITO) electrode. To fabricate the PEC biosensor, Bi₂MoO₆ nanoparticles were prepared by a hydrothermal method and coated on a bare ITO electrode. When L-Cys existed, Bi₂S₃ was formed in situ on the interface of the Bi₂MoO₆/ITO electrode by a chemical displacement reaction. Under the visible light irradiation, the Bi₂MoO₆–Bi₂S₃/ITO electrode exhibited evident enhancement in photocurrent response compared with the Bi₂MoO₆/ITO electrode, owing to the signal-increased sensing system and the excellent property of the formed Bi₂MoO₆–Bi₂S₃ heterostructure such as the widened light absorption range and efficient separation of photo-induced electron–hole pairs. Under the optimal conditions, the sensor for L-Cys detection has a linear range from 5.0 × 10⁻¹¹ to 1.0 × 10⁻⁴ mol L⁻¹ and a detection limit of 5.0 × 10⁻¹² mol L⁻¹. The recoveries ranging from 90.0% to 110.0% for determining L-Cys in human serum samples validated the applicability of the biosensor. This strategy not only provides a method for L-Cys detection but also broadens the application of the PEC bioanalysis based on in situ formation of photoactive materials.

Oxidized titanium carbide MXene-enabled photoelectrochemical sensor for quantifying synergistic interaction of ascorbic acid based antioxidants system

Antioxidants can protect organization from damage by scavenging of free radicals. When two kinds of antioxidants are consumed together, the total antioxidant capacity might be enhanced via synergistic interactions. Herein, we develop a simple, direct, and effective strategy to quantify the synergistic interaction between ascorbic acid (AA) and other different antioxidants by photoelectrochemical (PEC) technology. MXene Ti₃C₂-TiO₂ composites fabricated via hydrogen peroxide oxidation were applied as sensing material for the antioxidants interaction study. Under excitation of 470 nm wavelength, the photogenerated electrons transfer from the conduction band of TiO₂ nanoparticles to the Ti₃C₂ layers, and the holes in TiO₂ can oxidize antioxidants, leading to an enhanced photocurrent as the detection signal. This PEC sensor exhibits a good linear range to AA concentrations from 12.48 to 521.33 μM as well as obvious antioxidants capability synergism. In particular, the photocurrents of AA + gallic acid (GA) and AA + chlorogenic acid (CHA) mixtures at 476.19 μM increase 1.95 and 2.35 times respectively comparing with the sum of photocurrents of AA and GA or CHA. It is found that the synergistic effect is mainly depending on the fact that AA with the low redox potential (0.246 V vs NHE) can reduce other antioxidants radical to promote regeneration, improving the overall antioxidant performance. Moreover, it is proved that the greater redox potential of antioxidants, the more obvious the synergistic effect. In addition, the sensor was used to real sample assay, which provides available information towards food nutrition analysis, health products design and quality inspection.

Metal composite oxides Bi2MoO6/IL membrane as matrix for constructing ultrasensitive electrochemical immunosensor

In the process of diagnosis and disease monitoring, it is important to quickly and easily detect protein biomarkers. The strategy reported here is an attempt to prepare Bi₂MoO₆ nanomaterial with new three-dimensional holes morphology surrounded by rod and sheet to construct a simple and sensitive sensing platform, where Bi₂MoO₆/ionic liquid (IL) composite was modified on the carbon paste electrode (CPE). In order to monitor the assembly process of human IgG immunosensors, a plurality of electrochemical tests such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) was executed. The obtained BSA/anti-IgG/GA/Bi₂MoO6/IL-CPE displayed prominent conductivity and high sensitivity in detecting human immunoglobulin G (human IgG). Under the optimal experimental conditions, the results by differential pulse voltammetry (DPV) showed that the constructed label-free IgG immunosensor can detect IgG in the range of 0.01 to 1000 ng mL^-1, and limit of detection (LOD) was 4 pg mL^-1. The immunosensor displayed good performances including selectivity, reproducibility, and stability. Based on preliminary experiments, Bi₂MoO₆ and its composite materials are very promising for the construction of a variety biosensors for the analysis of other biological substances. Graphical abstract.

New Bi2MoO6 nano-shapes toward ultrasensitive enzymeless glucose tracing: Synergetic effect of the Bi-Mo association

In a novel approach, an efficient non-enzymatic glucose sensor based on pure phase of aurivillius bismuth molybdate (BM or γ-Bi₂MoO₆) mixed metal oxides is reported. Three BM samples were synthesized, with/without l-cysteine (Cys) and dodecylamine (DDA) as additives, leading to different shapes: bullet (BM-C), confetti (BM-2Cys) and candy (BM-2DDA). The morphology and purity of the structures were confirmed by FE-SEM images and XRD. In order to investigate the sensor application, the samples were integrated on reduced graphene oxide and incorporated into simple and inexpensive glassy carbon electrode (GCE) without using any polyvinylpyrrolidone (PVP) or Nafion. To perform cyclic voltammetry experiments, all three biosensors were measured in PBS solution (pH = 7) in ±1.5 voltage range and 50 mV s^-1 scan rate. Glucose identification by the synthesized composites is an obvious sign of their high efficiency. According to chronoamperomograms, the best sensitivity of 3050 μA L mmol^-1 cm^-2 with linear range of 0.02-0.14 mmol L^-1, low detection limit (LOD) of 0.004 mmol L^-1 and the signal/noise equal to 3 was achieved by BM-2DDA/rGO/GCE biosensor and its speedy amperometric response is less than 5 s. This biosensor showed impressive selectivity, repeatability and reproducibility results besides it maintains its stability considerably in great percentage of 98.5% after eight weeks. Also it showed prolonged stability after 50 min.

Biosensors and Sensing Systems for Rapid Analysis of Phenolic Compounds from Plants: A Comprehensive Review

Phenolic compounds are secondary metabolites frequently found in plants that exhibit many different effects on human health. Because of the relevant bioactivity, their identification and quantification in agro-food matrices as well as in biological samples are a fundamental issue in the field of quality control of food and food supplements, and clinical analysis. In this review, a critical selection of sensors and biosensors for rapid and selective detection of phenolic compounds is discussed. Sensors based on electrochemistry, photoelectrochemistry, fluorescence, and colorimetry are discussed including devices with or without specific recognition elements, such as biomolecules, enzymes and molecularly imprinted materials. Systems that have been tested on real matrices are prevalently considered but also techniques that show potential development in the field.

Novel Electron Donor Encapsulation Assay Based on the Split-type Photoelectrochemical Interface

In this research, a controlled-release photoelectrochemical (PEC) immunosensor is proposed on the basis of a novel encapsulation strategy by all-inorganic semiconductor materials. The controlled-release transmit system has been prepared and represented on account of a group-functional mesoporous silica nanosphere (MSN), utilizing surface-functionalized cadmium sulfide (CdS) nanoparticles as mobilizable caps to encapsulate a PEC electron donor ascorbic acid (AA) within the MSN mesoporous structure. This encapsulation strategy proceeds without any enzyme and acid/alkali to achieve the release of an electron donor. The complex is formed by encapsulating AA within MSN with CdS (CdS@MSN-AA) as a signal amplifier labeled on the secondary antibody. In addition, the immunological recognition process was performed in a 96-well plate, and the reciprocal interference between biorecognition and PEC analysis could be eliminated through a split-type framework. Bi₂S₃-sensitized porous In₂O₃ nanoparticles as a substrate matrix provide basic PEC response. The developed sensor exhibited a mensurable output of procalcitonin (PCT) concentration (as an example) in the detection range of 0.001-200 ng/mL along with a limit of detection of 0.31 pg/mL. Featuring the novel method for electron release, this sensitive PEC strategy provides an innovative way for the potential application for other targets.

Oxygen vacancy enhanced photoelectrochemical performance of Bi2MoO6/B, N co-doped graphene for fabricating lincomycin aptasensor

Oxygen defect-engineered is an important strategy to improve the photoelectric activity of materials. Herein, a facile one-pot solvothermal method was utilized to synthesize visible light-responsive photoactive Bi₂MoO₆ nanoparticles anchored boron and nitrogen co-doped graphene (BNG) nanosheets nanocomposites with oxygen vacancy. The incorporation of BNG nanosheets increased the oxygen vacancies amounts on Bi₂MoO₆ remarkably, and the presences of oxygen vacancies can be beneficial to broaden the absorption range. The absorption edge of Bi₂MoO₆/BNG was widened from 500 nm to 550 nm compared to Bi₂MoO₆, and the charge transfer was accelerated to improve the photoactive of Bi₂MoO₆/BNG. Under visible light illumination, the photoelectrochemical (PEC) response of the as-prepared Bi₂MoO₆/BNG was 11.6-fold, 6.7-fold, 3.1-fold and 2.4-fold higher than that of pristine Bi₂MoO₆, Bi₂MoO₆/graphene, Bi₂MoO₆/nitrogen doped graphene and Bi₂MoO₆/boron doped graphene. Using Bi₂MoO₆/BNG nanocomposites with the superior PEC performance as photoactive materials in combination with specifically recognized lincomycin (LIN) aptamer, a highly efficient PEC aptasensor was successfully constructed for sensitive analysis of LIN. Under optimal conditions, the proposed PEC aptasensor exhibited excellent analytical performance for LIN with a wide linear response of 1 × 10^-11 to 1 × 10^-6 mol L^-1 along with a low detection limit of 3.7 × 10^-12 mol L^-1 (defined as S/N = 3). The as-prepared Bi₂MoO₆/BNG nanocomposites exhibit excellent visible light response and PEC performance, indicating its potential applications in PEC biosensor.

Recent developments of photoelectrochemical biosensors for food analysis

Recent developments of photoelectrochemical biosensors for food analysis are summarized and the future prospects in this field are discussed.

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.

Label-free photoelectrochemical aptasensor for tetracycline detection based on cerium doped CdS sensitized BiYWO6

A novel photoelectrochemical (PEC) aptasensor based on cerium (Ce) doped CdS modified graphene (G)/BiYWO₆ was designed, which exhibits enhanced PEC intensity compared with pure BiYWO₆, G/BiYWO₃ and BiYWO₆/Ce:CdS. In this scenario, ascorbic acid (AA) was exploited as an efficient and non-poisonous electron donor for scavenging photogenerated holes. The doping of Ce in CdS promoted its visible light absorption range and facilitated the charge transfer rate as well as hindered the h⁺/e^- recombination. Moreover, the combination of G further promoted the electron carrier separation and transfer process due to its excellent electron collection and shuttling characteristic. Thus, the G/BiYWO₆/Ce:CdS heterostructure was successfully served as a matrix for the PEC detection of tetracycline (Tc) at 0 V (vs Hg/Hg₂Cl₂). Under optimal conditions, the PEC aptasensor could offer a sensitive and specific detection limit (3 S/N) of Tc down to 0.01 ng/mL, as well as acceptable reproducibility, selectivity and storage stability, which opened up a promising pathway for the development of PEC biosensors.