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Signal amplification strategies are of great interest in photoelectrochemical (PEC) sensing research. Herein, we explored a novel approach whereby hole transfer was accelerated from the photosensitive material Blue-TiO 2 (B-TiO 2) to the hole mediator N-hydroxyphthalimide (NHPI). Simultaneously, the introduction of the organic molecule NHPI can promote the efficiency of visible light absorption and expand the absorption range of B-TiO 2. Under visible light irradiation, the photocurrent value of NHPI/B-TiO 2 is 2.7-fold larger than that of B-TiO 2 , which can be ascribed to the acceleration of hole transfer by NHPI. More specifically, NHPI acts as a hole mediator, which effectively transfers photo-generated holes from the valence band (VB) of B-TiO 2 to NHPI. NHPI can be oxidized to phthalimide-N-oxyl radical (PINO*), thereby causing inhibition of photo-generated carrier recombination and enhancement of the photocurrent. Furthermore, a PEC aptasensor for the sensitive detection of diazinon (DIA) was constructed by combining specific aptamers on an NHPI/B-TiO 2 nanocomposite surface. The oxidation product of NHPI, PINO*, oxidizes the DIA captured by the aptamer. Under optimized experimental conditions, the linear range for DIA detection was 0.1–1000 nM, and the detection limit of the NHPI/B-TiO 2 nanocomposite aptamer sensing was 0.03 nM (S/N = 3). Therefore, this proposed method involving the hole mediator can be used as a new strategy to improve the performance of PEC. [Display omitted] • A new strategy for enhancing photoelectrochemical (PEC) signals was developed. • Hole mediator can accelerate photo-generated holes transfer. • Hole mediator can be oxidized by photo-generated holes and promote redox reaction. • Organic molecule have the advantage of high visible light absorption efficiency. • The PEC aptasensor exhibited excellent selectivity and sensitivity for Diazinon. [ABSTRACT FROM AUTHOR]

Synopsis: Diagram of one-step synthesis of core-shell LaFeO 3 @g-C 3 N 4 heterostructure and photoelectrochemical and optical absorption properties of various materials. • The LaFeO 3 @g-C 3 N 4 heterostructure was synthesized by facile one-step method. • The LaFeO 3 @g-C 3 N 4 showed superior PEC properties than LaFeO 3 /g-C 3 N 4. • A PEC aptasensor was constructed for detection of streptomycin. • The proposed aptasensor has a wide linear range and low detection limits. The development of core-shell heterostructure photoactive materials with high visible light response and charge separation efficiency is of great significance. Herein, we prepared LaFeO 3 @g-C 3 N 4 p-n heterojunction with core-shell structure by using facile one-step method. As a contrast, g-C 3 N 4 nanosheets decorated with LaFeO 3 nanoparticles (LaFeO 3 /g-C 3 N 4) were synthesized by a reported method. The LaFeO 3 @g-C 3 N 4 heterostructure boosted the visible light response and effectively separated charge carriers compared to LaFeO 3 /g-C 3 N 4. Moreover, for LaFeO 3 @g-C 3 N 4 heterostructure, the interaction of core-shell interface and synergistic effect of p-n heterojunction made photoelectrochemical (PEC) properties more stable and excellent. Concretely, the absorption band edge of LaFeO 3 @g-C 3 N 4 heterostructure was about 700 nm, which was wider than LaFeO 3 /g-C 3 N 4. Additionally, the photocurrent signal of LaFeO 3 @g-C 3 N 4 heterostructure was 2.3-fold higher than that of LaFeO 3 /g-C 3 N 4. Thus, on the basis of the prominent PEC performance of LaFeO 3 @g-C 3 N 4 heterostructure, we constructed a PEC aptasensor to detect streptomycin (STR) sensitively and selectively. The aptasensor revealed a wide linear concentration range from 0.01 nM to 10000 nM of STR, with a low detection limit of 0.0033 nM (S/N = 3). The fabricated aptasensor had excellent stability, practicability, and reproducibility, laying a good foundation for STR detection in other analytical fields. [ABSTRACT FROM AUTHOR]

Abstract Rational design and fabrication of Z-scheme visible-light-driven photoactive materials have drawn much attention owing to their great potential in handling environment and energy crisis. In this work, Z-scheme Bi 2 S 3 /nitrogen-doped graphene quantum dots (NGQDs) with superior photoelectric conversion efficiency were designed and fabricated, which demonstrated enhanced photoactivity compared with Bi 2 S 3 owing to the improved separation efficiency of photogenerated electron and hole pairs. The emphasis was put on designing Z-scheme Bi 2 S 3 /NGQDs, and then the mechanism of Z-scheme charge transfer mode was verified by the electron spin resonance (ESR) technique. On this basis, the proposed sensor exhibited a wide linear range of 0.1–120 nM and a detection limit of 0.03 nM (S/N = 3) for SDM, with high sensitivity (0.075 μA nM –1), good selectivity and stability. Moreover, the proposed PEC aptasensor using Bi 2 S 3 /NGQDs as the photoelectrode achieved sensitive and selective determination of sulfadimethoxine in milk samples. This work could provide some ideas for designing other Z-scheme photoactive species and insights into the charge transfer mechanism of Z-scheme. Furthermore, the promising applicability of PEC aptasensor using photoactive species could be extended to other accurate monitoring for contaminants. Highlights • A Z-scheme type Bi 2 S 3 /NGQDs heterojiunction was designed and construced. • The resulted Bi 2 S 3 /NGQDs showed superior photo-electric conversion efficiency. • ESR technique was used to verify the Z-scheme charge transfer mode of Bi 2 S 3 /NGQDs. • A PEC sulfadimethoxine aptasensor was fabricated based on photoactive Bi 2 S 3 /NGQDs. • The proposed PEC aptasensor exhibited a wider linear range and lower detection limit. [ABSTRACT FROM AUTHOR]

Abstract Developing effective sensing method for trace analysis of ampicillin (AMP) is urgent and significant due to its residue possess serious threats to human health. Herein, a p-n heterojunction, on the basis of p-type BiFeO 3 nanoparticles coupled n-typed ultrathin graphite-like carbon nitride (utg-C 3 N 4) nanosheets, has been designed and synthesized via a simple electrostatic interaction strategy. Such p-n heterojunction has two advantages: one is capable to narrow the band gap of photoactive materials from 2.20 eV of BiFeO 3 down to 2.04 eV of BiFeO 3 /utg-C 3 N 4 , leading to improve the efficiency of visible light utilization; and the other is to facilitate the charge separation rate, resulting in the boosted photoelectrochemical (PEC) performance of BiFeO 3 /utg-C 3 N 4. Under visible light illumination, the photocurrent of the resulted BiFeO 3 /utg-C 3 N 4 was 7.0-fold enhanced than that of pure BiFeO 3 nanoparticles, and indeed 2.3-fold enhanced comparing to BiFeO 3 /bulk-C 3 N 4. Based on excellent PEC properties of BiFeO 3 /utg-C 3 N 4 , an on-off-on PEC aptasensor was successfully fabricated for ampicillin (AMP) determination with highly selectivity and sensitivity. The fabricated PEC aptasensor exhibited excellent PEC performance with a broad linear in the range from 1 × 10–12 mol L–1 to 1 × 10−6 mol L–1 as well as a low detection limit of 3.3 × 10–13 mol L–1 (S/N = 3), and also good feasibility in real sample. The excellent analytical performance indicated that PEC aptasensor on the basis of the visible light driven BiFeO 3 /utg-C 3 N 4 heterojunction can provide a promising biosensor platform for sensitive detection AMP in food and environment analysis. Highlights • The BiFeO 3 /utg-C 3 N 4 p-n heterostructure was facile constructed by electrostatic interaction. • The photocurrent intensity BiFeO 3 /utg-C 3 N 4 exhibits 7.0-fold and 2.3-fold enhanced than BiFeO 3 and BiFeO 3 /bulk-C 3 N 4. • An on-off-on PEC ampicillin aptasensor was successfully fabricated. • The proposed sensitive ampicillin aptasensor exhibits a wide linear range and low detection limit. [ABSTRACT FROM AUTHOR]

Synopsis: Successful preparation of VOPc/CN photoactive materials and construction of PEC aptasensor for DCF detection. • Facile method with easy fabrication enabled the visible/NIR light response PEC sensor for rapid DCF detection. • VOPc/CN nanocomposites was first used as photoactive materials. • VOPc/CN based on VOPc sensitizing CN extend spectral range to visible/ NIR light region. • VOPc/CN photoactive materials demonstrated improved photoelectric conversion efficiency. • This biosensor showed a good sensitivity and a wide linear range. A novel photoelectrochemical (PEC) aptasensor for diclofenac detection, based on visible/near-infrared (vis/NIR) light-responsive vanadyl-phthalocyanine/graphitic carbon nitrid nanosheet (VOPc/CN) nanocomposites, was successfully fabricated. In this work, the first coupling of CN and VOPc with a facile solution–phase method was prepared and applied to PEC sensing. The UV–vis diff ;use reflection spectra (DRS) indicated that VOPc is an excellent photosensitizer when applied to the surface of CN. It promoted CN light absorption to the visible-NIR region, which greatly enhanced the light excitation capability. The PEC signal of the VOPc/CN nanocomposites improved 2.7 and 12.42-fold compared with pure VOPc and CN, respectively, indicating that VOPc/CN nanocomposites have good photoelectric activity and enhanced photo-to-current conversion efficiency. As a result, VOPc sensitized CN was introduced as a covalent immobilizing PEC aptasensor for the sensitive and selective determination of diclofenac (DCF). Under optimal conditions, the fabricated PEC biosensor exhibited good PEC performances with high sensitivity, a low detection limit of 0.03 nM (S/N = 3) and a wide linear response, in the range of 0.1-500 nM. This was due to the specific interaction between DCF and the aptamer. It is concluded that VOPc/CN nanocomposites are potentially promising photoactive materials for applications in PEC biosensors, as well as for photocatalysis and other related fields. [ABSTRACT FROM AUTHOR]

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

Dye sensitization is an alternative strategy to improve photoelectric activity of semiconductors and, particularly, to enhance the activity towards visible light domain. Herein, an artificial Z-scheme bipyridine ruthenium (Ru(bpy) 3 2+) sensitizing narrow-gap bismuth oxy-iodide (BiOI) microspheres was constructed by a simple electrostatic interaction strategy for the first time. The electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) analysis showed that this design of such Z-scheme structure was helpful to enhance the interfacial charge transfer and improve the photoelectric conversion efficiency. In addition, due to the sensitization of Ru(bpy) 3 2+, the band gap was narrowed from 1.8 eV of BiOI microspheres to 1.3 eV of BiOI/Ru(bpy) 3 2+ microspheres, leading to improve the utilization of visible light. So that, the photocurrent of the resulted BiOI/Ru(bpy) 3 2+ was 13.0 times that of pure BiOI microspheres. In view of the outstanding photoelectrochemical (PEC) performance of BiOI/Ru(bpy) 3 2+ and the high specificity of the aptamer, the PEC aptasensor for ampicillin (AMP) merits the excellent detection performance including a broad linear ranging from 1 × 10–7 nM to 100 nM as well as a low detection limit of 3.3 × 10–8 nM (S/N = 3). This work not only provides a novel way to construct and design highly efficient photoactive materials for PEC detection, but also broadens the application of Z-scheme in the field of sensing. • BiOI/Ru(bpy) 3 2+ microspheres were successfully prepared, showing a 13-fold photocurrent intensity compared to pure BiOI. • The Z-scheme configuration was helpful to enhance the interfacial charge transfer. • As a sensitizer, Ru(bpy) 3 2+ extended the spectral response of BiOI/Ru(bpy) 3 2+, thus improving the visible light utilization. • The fabricated PEC aptasensor exhibited good selectivity and sensitivity for ampicillin detection. [ABSTRACT FROM AUTHOR]