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.

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.