Waste Biomass-Mediated Synthesis of TiO2/P, K-Containing Grapefruit Peel Biochar Composites with Enhanced Photocatalytic Activity.

In this study, TiO2/P, K-containing grapefruit peel biochar (TiO2/P, K-PC) composites were synthesized in situ biomimetically using grapefruit peel as the bio-template and carbon source and tetrabutyl titanate as the titanium source. This was achieved using the two-step rotary impregnation-calcination method. Adjusting the calcination temperature of the sample in an air atmosphere could regulate the mass ratio of TiO2 to carbon. The prepared samples were subjected to an analysis of their compositions, structures, morphologies, and properties. It demonstrated that the prepared samples were complexes of anatase TiO2 and P, K-containing carbon, with the presence of graphitic carbon. They possessed a unique morphological structure with abundant pores and a large surface area. The grapefruit peel powder played a crucial role in the induction and assembly of TiO2/P, K-PC composites. The sample PCT-400-550 had the best photocatalytic activity, with the degradation rate of RhB, MO, and MB dye solutions reaching more than 99% within 30 min, with satisfactory cyclic stability. The outstanding photocatalytic activity can be credited to its unique morphology and the efficient collaboration between TiO2 and P, K-containing biochar.

Design of NiS@Ni3S2/CdS heterostructure with intimate contact interface for sensitive photoelectrochemical detection of lincomycin.

Owing to their internal electric field effect and abundant photo-induced carriers, photoactive heterostructured materials are considered a feasible approach to improve the sensitivity of a photoelectrochemical (PEC) sensor. Herein, a novel NiS@Ni3S2/CdS heterostructure composite is derived from Ni-loaded zeolitic imidazolate framework (Ni-ZIF). The PEC experiments showed the NiS@Ni3S2/CdS composite exhibits superior photocurrent response than NiS@Ni3S2 and CdS. This is attributed to the fact that the type II heterojunction of NiS@Ni3S2/CdS with a tightly connected interface reduces the transport distance of carriers and facilitates electron-hole separation. Next, using the NiS@Ni3S2/CdS modified electrode, an aptamer/glutaraldehyde/chitosan/NiS@Ni3S2/CdS/ITO PEC biosensor is developed, which exhibits excellent sensitivity for lincomycin (Lin) detection with a wide linear range (0.0001 âˆ¼ 1.25 nM) and a low detection limit of 0.067 pM. The prepared sensor is further employed to monitor Lin in the actual milk. The results confirm that the prepared sensing electrode displays good selectivity, repeatability and stability.

Novel design constructed In2S3@SnO2 hollow heterojunctions by insufficiently etched MOFs as framework for photoelectrochemical bioanalysis.

Compared to sufficiently etched MOFs materials, insufficiently etched MOFs materials tend to display unsatisfactory performance due to their immature structure and have been eliminated from scientific research. Herein, this work reported a novel In2S3@SnO2 heterojunction (In2S3@SnO2-HSHT) materials, which were stably synthesized in high temperature aqueous environment and equipped extraordinary photoelectrochemical (PEC) properties, fabricated by a succinct hydrothermal synthesis method using insufficiently etched MIL-68 as a self-sacrificing template. Compared with the control groups and In2S3@SnO2 heterojunctions with collapse morphology synthesized by sufficiently etched MIL-68 in high temperature aqueous environment, In2S3@SnO2-HSHT synthesized from insufficiently etched MIL-68 as a template had a massively enhanced light-harvesting capability and generated more photoinduced charge carriers due to its well-preserved hollow structure. Therefore, based on outstanding PEC performance of In2S3@SnO2-HSHT, the established PEC label-free signal-off immunosensor to detect CYFRA 21-1, revealing vivid selectivity, stability, and reproducibility. This novel strategy adopted the insufficient chemical etching method neglected by the mainstream chemical etching approaches, which solved the challenge that the stability of the sufficient etched MOFs with hollow structure cannot be maintained under the subsequent high temperature aqueous reaction conditions, and was further applied to the design of hollow heterojunction materials for photoelectrochemical fields.

A highly sensitive photoelectrochemical biosensor for CEA analysis based on hollow NiS@NiO/TiO2 composite with typal p-n heterostructure.

Heterostructured construction is regarded as a valuable approach to improve photoelectrochemical (PEC) performances. Herein, porous hollow NiS@NiO spheres were prepared derived from the Ni(TCY) MOFs precursor. Photoactive TiO2 was coupled with as-prepared NiS@NiO to form a close heterojunction interface of NiS@NiO/TiO2. NiS@NiO/TiO2 modified ITO electrode (NiS@NiO/TiO2/ITO) displayed fiercely enhanced photocurrent response, which was 4687-fold than that of NiS@NiO/ITO (0.008 µA) and 8.5-fold than that of TiO2/ITO (4.41 µA), respectively. Remarkable PEC property could be ascribed to the hollow NiS@NiO spheres with thin-shell structure provided there is a larger active surface area for harvesting the visible light. Most importantly, the p-n type NiS@NiO/TiO2 heterojunction could lead to generating more photo-excited charge carriers (e-/h+) and efficiently hinder the recombination of carriers, resulting in significantly augmented photocurrent output. Based on this outstanding PEC property, NiS@NiO/TiO2/ITO electrode fabricated sensing platform (BSA/anti-CEA/NiS@NiO/TiO2/ITO, BSA=Bovine serum albumin) exhibited high sensitivity for monitoring CEA (Carcinoembryonic antigen). Wide linear detection range was from 0.001 to 45 ng mL-1 and with a low detection limit of 1.67 × 10-4 ng mL-1 (S/N = 3). Prepared biosensors also showed good reproducibility, stability and had satisfying specificity. Thus, the proposed NiS@NiO/TiO2 heterostructured composite afforded well-design and synthesis strategy for constructing high-performance photoactive materials from MOFs-derivate.

In-situ preparation of hollow CdCoS2 heterojunction with enhanced photocurrent response for highly photoelectrochemical sensing of organophosphorus pesticides.

In this study, a porous hollow CdCoS2(2) microsphere was synthesized based on the ZIF-67-S MOFs derived method of sulfurization reaction and calcination process. Under visible light irradiation, the resulting CdCoS2(2) composite showed a markedly enhanced photoelectrochemical (PEC) response. The photocurrent value of the CdCoS2(2) modified ITO electrode was 93-fold and 41-fold than that of CoS and CdS materials, respectively. Promoting the photo-absorption ability by internal multilight scattering/reflection was due to the porous and hollow nature of CdCoS2(2). Furthermore, obtained CdCoS2(2) heterostructure in-situ with a close contact interface could facilitate the separation/migration of photo-induced carriers. The CdCoS2(2) was also mixed with Ag nanoparticles (NPs) to further improve the PEC response. Acetylcholinesterase (AChE) as a bio-recognition molecule was immobilized on the glutaraldehyde-chitosan (GLD-CS) modified CdCoS2(2)@Ag electrode surface by cross-linking effect. AChE could hydrolyze the acetylcholine chloride (ATCl) to produce an electron donor of thiocholine which led to the elevated photocurrent output. When the bioactivity of AChE was inhibited by the organophosphate pesticides (chlorpyrifos as substrate), the reduced production of thiocholine resulted in a decline in photocurrent. Under optimal conditions, the structured AChE/GLD-CS/CdCoS2(2)@Ag/ITO sensing platform was successfully achieved for chlorpyrifos detection. The wide linear response range was from 0.001 to 270 µg mL-1 and with a low detection limit of 0.57 ng mL-1. The proposed PEC biosensor also exhibited excellent selectivity and good stability, demonstrating the designed porous hollow CdCoS2(2)@Ag heterostructured composite promised to be a great application in the PEC sensors.

In-situ construction of hollow double-shelled CoSx@CdS nanocages with prominent photoelectric response for highly sensitive photoelectrochemical biosensor.

In this work, we demonstrate a delicate design and construction of hollow double-shelled CoSx@CdS nanocages (CoSx@CdS-HDSNCs) as an efficient and stable photoactive material of photoelectrochemical (PEC) biosensor for detecting cardiac troponin I (cTnI). The novel self-templated strategy started with ZIF-67, in which two distinct sulfide semiconductors were integrated into a hollow heterojunction with uniform interfacial contacts after sequential anion and cation exchange. The unique thin double shell hollow structure, suitable energy band arrangement and stable electron transmission vastly enhanced the ability of light capture and photogenerated electron-hole separation of biosensor. Subsequently, the photoelectric performance of the heterojunction was further enhanced by the deposition of Au nanoparticles (NPs) on the surface of the CoSx@CdS-HDSNCs resulting in surface plasmon resonance (SPR) effect. Based on the excellent CoSx@CdS-HDSNCs, the biosensor exhibits a high sensitivity for detection of cTnI with a wide linear range (0.00016-16 ng mL-1) and low detection limit (38.6 fg mL-1). Besides, the PEC biosensor exhibited satisfactory stability, selectivity, and reproducibility in human serum. And more importantly, our work may provide more unique inspiration for the design of photoactive materials for the future PEC sensing applications.

Sensitive photoelectrochemical detection of colitoxin DNA based on NCDs@CuO/ZnO heterostructured nanocomposites with efficient separation capacity of photo-induced carriers.

A metal-organic framework (MOF) of Cu-TPA (terephthalic acid) microsphere was prepared, followed by calcinating the MOF precursor of Cu-TPA/ZIF-8 mixture to obtain the CuO/ZnO. N-doped carbon dots (NCDs) were employed to combine the CuO/ZnO composite to form a tripartite heterostructured architecture of NCDs@CuO/ZnO, which led to a fierce enlargement of the photocurrent response. This  was ascribed to the thinner-shell structure of the CuO microsphere and the fact that hollow ZnO particles could sharply promote the incidence intensity of visible light. The more porous defectiveness exposed on CuO/ZnO surface was in favor of rapidly infiltrating electrolyte ions. The p-n type CuO/ZnO composite with more contact interface could abridge the transfer distance of photo-induced electron (e-1)/hole (h+) pairs and repress their recombination availably. NCDs not only could boost electron transfer rate on the electrode interface but also successfully sensitized the CuO/ZnO composite, which resulted in high conversion efficiency of photon-to-electron. The probe DNA (S1) was firmly assembled on the modified ITO electrode surface (S1/NCDs@CuO/ZnO) through an amidation reaction. Under optimal conditions, the prepared DNA biosensor displayed a wide linear range of 1.0 × 10-6 ~ 7.5 × 10-1 nM and a low limit of detection (LOD) of 1.81 × 10-7 nM for colitoxin DNA (S2) measure, which exhibited a better photoelectrochemistry (PEC) analysis performance than that obtained by differential pulse voltammetry techniques. The relative standard deviation (RSD) of the sensing platform for target DNA detection of 5.0 × 10-2 nM was 6.3%. This proposed DNA biosensor also showed good selectivity, stability, and reproducibility, demonstrating that the well-designed and synthesized photoactive materials of NCDs@CuO/ZnO are promising candidates for PEC analysis.

Rationally constructed ZnCdS-HDCs@In2S3-HNRs double-hollow heterojunction with promoted light capture capability for photoelectrochemical biosensing.

The construction of novel heterojunction is regarded as an operative scheme to promote the transport of photogenerated carriers and reduce electron-hole pair recombination to enhance the photoelectrochemical (PEC) performances. Herein, ZnCdS hollow dodecahedral nanocages (ZnCdS-HDCs) and In2S3 hollow nanorods (In2S3-HNRs), which were derived from two different of metal-organic frameworks (MOFs) by solvothermal sulfidation method and were constructed an original double-hollow heterostructure ZnCdS-HDCs@In2S3-HNRs. The intrinsic mechanism of In2S3-HNRs benefiting from unique morphology to boost the photochemical properties under visible light irradiation was illustrated. Meanwhile, the mechanism of the novel type II heterojunction with staggered matching levels was revealed, which could effectively restrict electron-hole pair reassociation separation, and accelerated charge separation and transfer. Therefore, based on the excellent PEC performance of ZnCdS- HDCs@In2S3-HNRs double-hollow heterostructure, a signal-off PEC biosensor platform without labeled was constructed for the detection of CA15-3, which manifested acceptable specificity, reproducibility and stability. Additionally, the expected PEC biosensors showed a linear response range from 1.0 × 10-5 to 10 U·mL-1 in addition to an ultralow detection limit of 3.78 × 10-6 U·mL-1. This study innovatively constructed and prepared a new double-hollow heterojunction material with superior PEC nature for the application of PEC biosensing, which exhibits a broad application prospect.

An enhanced photoelectrochemical biosensor for colitoxin DNA based on HKUST-1/TiO2 and derived HKUST-CuO/TiO2 heterogeneous composites.

HKUST-1 MOFs and its derivative HKUST-CuO were coupled with TiO2 nanoparticles to form the heterogeneous composites of HKUST-1/TiO2 and HKUST-CuO/TiO2 based on their well-suitable bandgap energies (Eg). Compared with mono-component HKUST-1 or HKUST-CuO, the prepared composites displayed photoelectrochemical (PEC) response due to the synergistic effect from their heterogeneous structure. Higher photocurrent response was obtained on HKUST-CuO/TiO2-modified ITO electrode (HKUST-CuO/TiO2/ITO), which could be attributed to the hollow structure with a thin shell of HKUST-CuO greatly enhancing visible spectra harvesting. The CuO component in HKUST-CuO not only could accelerate electron transfer on the heterojunction interface but also effectively separate the photo-generated charge carriers (e-1/h+). Based on the excellent PEC performance of prepared photoactive composite material, under visible-light excitation (λ ≥ 420 nm) and with a working potential of 0 V (vs. Ag/AgCl), the S1 (probe DNA)/HKUST-CuO/TiO2/ITO PEC platform was successfully fabricated for colitoxin DNA detection without using ascorbic acid (AA) as an electron donor. Compared with the analysis results on S1/HKUST-1/TiO2/ITO electrode, S1/HKUST-CuO/TiO2/ITO displayed a wider linear response range from 1.0 × 10-6 to 4.0 × 10-1 nM with a lower detection limit of 3.73 × 10-7 nM (S/N = 3), the linear regression equation was ΔI (10-6 A) =0.5549-0.1858 log (CS2/M), which confirmed the HKUST-CuO could improve sensitivity because of its prominent PEC property. The relative standard deviation (RSD) of the PEC sensor for target DNA detection of 2.0 × 10-4 nM was 7.4%. The proposed DNA biosensor also possessed good specificity and stability. Hence, this reported work was a promising strategy for molecular diagnosis in the bio-analysis field. (A) Schematic illustration of the preparation process of the proposed PEC biosensors for colitoxin DNA detection. (B) The preparation process of HKUST-1 and HKUST-CuO.

Design of ultrathin nanosheet subunits ZnIn2S4 hollow nanocages with enhanced photoelectric conversion for ultrasensitive photoelectrochemical sensing.

Herein, a high-efficiency photoactive material, hollow ZnIn2S4 nanocages (ZIS-HNCs) composed of ultrathin nanosheets were creatively synthesized via a metal-organic framework (MOF) derived solvothermal method. It had been specified the underlying mechanism of the ZIS-HNCs evolution under the MOF templated surface. Subsequently, the obtained ZIS-HNCs combined with annealing TiO2 modified electrode (ZIS-HNCs@TiO2), and the ZIS-HNCs@TiO2 exhibited intense transient photocurrent. The enhanced photocurrent signal benefited from the multiple light capture effect of ZIS-HNCs, ultrathin nanosheet subunits of ZIS-HNCs, and typical type Ⅱ heterojunction, which could effectively retard the photoexcited electron-hole pairs recombination, and accelerated charge separation and transfer. Taking antibiotic lincomycin (Lin) as a model, a signal-off photoelectrochemical (PEC) aptasensor based on the ZIS-HNCs@TiO2 was established and manifested a high sensitive detection for Lin with a linear response range from 0.0001 to 0.1 nM as well as an ultralow detection limit of 0.084 pM. Additionally, the proposed PEC aptasensor showed acceptable stability and remarkable selectivity. Therefore, this study provides a promising strategy to design nanomaterials with superior photoelectric activity for PEC sensing applications.

An electrochemical sensor for gallic acid based on Fe2O3/electro-reduced graphene oxide composite: Estimation for the antioxidant capacity index of wines.

A highly sensitive electrochemical sensor for gallic acid (GA), an important polyphenolic compound, was fabricated using the hybrid material of chitosan (CS), fishbone-shaped Fe2O3 (fFe2O3), and electrochemically reduced graphene oxide (ERGO) as the sensing matrix. The electrochemical characterization experiments showed that the CS-fFe2O3-ERGO modified glassy carbon electrode (CS-fFe2O3-ERGO/GCE) had large surface area, excellent electronic conductivity and high stability. The GA presented a superior electrochemical response on CS-fFe2O3-ERGO/GCE in comparison with the single-component modified electrode. The electrochemical mechanism and optimal test conditions of GA on the electrode surface were carefully investigated. Under the optimal conditions, the oxidation peak currents in differential pulse voltammetry (DPV) experiments exhibited a good linear relationship with the logarithmic values of GA concentration over the range from 1.0×10(-6)M to 1.0×10(-4)M. Based on signal-to-noise (S/N) characteristic of 3, the detection limit was estimated to be 1.5×10(-7)M. The proposed sensor has also been applied for estimating the antioxidant capacity index of real samples of red and white wines.

An ultrasensitive DNA biosensor based on covalent immobilization of probe DNA on fern leaf-like α-Fe2O3 and chitosan Hybrid film using terephthalaldehyde as arm-linker.

In this work, a novel electrochemical DNA biosensor has been developed based on the hybrid film of fern leaf-like α-Fe2O3 microparticles and chitosan (CS). The fern leaf-like α-Fe2O3 microparticles were synthesized via a facile template-free hydrothermal method, and their morphologies were characterized by X-ray diffraction, energy dispersive spectrometry, scanning electron microscope, and transmission electron microscope. Electrochemical characterization assays revealed that the hybrid film modified electrode had remarkable synergistic effects of the large accessible surface area and high electrical conductivity of semiconductive Fe2O3, and the good film stability of CS. Based on the rich amino groups on CS, the CS-Fe2O3 hybrid film was employed as a functional matrix for probe DNA immobilization using terephthalaldehyde (TPA) as a bifunctional arm-linker. The hybridization capacity of the developed biosensor was evaluated with electrochemical impedance spectroscopy (EIS) using [Fe(CN)6](3-/4-) as the indicating probe. A wide dynamic detection range from 1.0 × 10(-14) to 1.0 × 10(-10)M with ultralow detection limit of 5.6 × 10(-15)M was achieved for the target DNA. The hybridization selectivity experiments further revealed that the biosensor could discriminate fully complementary sequences from one-base mismatched, three-base mismatched, and non-complementary sequences. Moreover, the biosensor showed the advantage of good regeneration ability and reproducibility.

Development of a novel electrochemical DNA biosensor based on elongated hexagonal-pyramid CdS and poly-isonicotinic acid composite film.

Three CdS materials with different shapes (i.e., irregular, rod-like, and elongated hexagonal-pyramid) were hydrothermally synthesized through controlling the molar ratio of Cd(2+) to thiourea. Electrochemical experiments showed that the elongated hexagonal-pyramid CdS (eh-CdS) modified on glassy carbon electrode (GCE) had the higher electrical conductivity than the other two forms. Then the eh-CdS modified GCE was further modified with a layer of poly-isonicotinic acid (PIA) through electro-polymerization in IA solution to enhance the stability and functionality of the interface. The layer-by-layer modification process was characterized by atomic force microscopy and electrochemistry. Then 5'-amino functionalized DNA was immobilized on the electrode surface through coupling with the carboxylic groups derived from PIA-eh-CdS composite film. The hybridization performance of the developed biosensor was evaluated using methylene blue as redox indicator, and the results showed that the peak currents of methylene blue varied with target concentrations in a wide linear range from 1.0 × 10(-14)M to 1.0 × 10(-9)M with a low detection limit of 3.9 × 10(-15)M. The biosensor also showed high stability and good discrimination ability to the one-base, three-base mismatched and non-complementary sequence.