HKUST-1 MOFs and its derivative HKUST-CuO were coupled with TiO 2 nanoparticles to form the heterogeneous composites of HKUST-1/TiO 2 and HKUST-CuO/TiO 2 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/TiO 2 -modified ITO electrode (HKUST-CuO/TiO 2 /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/TiO 2 /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/TiO 2 /ITO electrode, S1/HKUST-CuO/TiO 2 /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 Δ I (10 −6 A) =0.5549–0.1858 log ( C S2 /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. Graphical abstract
(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.
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. Graphical abstract
Rugby-ball-shaped CoS2 (rCoS2) submicroparticles have been synthesized via a simple hydrothermal reaction. The rCoS2 submicroparticles were then casted on a glassy carbon electrode and served as a highly conductive and large surface area platform for the electrosynthesis of poly(2-thiophenesulfonyl chloride) (pTSC), using 2-thiophenesulfonyl chloride as the monomer. The stepwise modification process was characterized by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and different electrochemical technologies. The stable pTSC layer was utilized as a functional interface to immobilize amino-modified probe DNA via a facile sulfonyl–amino condensation reaction, without the assistance of any other cross-linkers. Because of the synergistic effect of rCoS2 and pTSC from the hybrid material, the developed DNA biosensor could detect target DNA over a wide dynamic range, from 1.0 × 10–13 to 1.0 × 10–7 M, with the detection limit down to 1.1 × 10–14 M. Benefiting from the steady electropolymerization film of pTSC and the stable sulfamide bond between the amino-modified DNA and pTSC, the biosensor also showed high stability, reusability, and reproducibility.
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