Integration of phosphate functionalized Pt/TiO2 and Ru(bpy)32+ sensitization for ultrasensitive assay of adenosine deaminase activity on a novel split-typed PEC aptasensor.

To date, it is still a challenge for high-performance photoelectrochemical (PEC) assay of low-abundance adenosine deaminase (ADA) in fundamental research and clinical diagnosis. Herein, phosphate-functionalized Pt/TiO2 (termed PO43-/Pt/TiO2) was prepared as ideal photoactive material to develop a split-typed PEC aptasensor for detection of ADA activity, coupled by a Ru(bpy)32+ sensitization strategy. We critically studied the effects of the PO43- and Ru(bpy)32+ on the detection signals, and discussed the signal-amplified mechanism. Specifically, hairpin-structured adenosine (AD) aptamer was splited into single chain via ADA-induced catalytic reaction, and subsequently hybridized with complementary DNA (cDNA, initially coating on magnetic beads). The in-situ formed double-stranded DNA (dsDNA) was further intercalated by more Ru(bpy)32+ to amplify the photocurrents. The resultant PEC biosensor showed a broader linear range of 0.05-100 U L-1 and a lower limit of detection (0.019 U L-1), which can fill the blank for analysis of ADA activity. This research would provide some valuable insights for building advanced PEC aptasensors in ADA-related research and clinical diagnosis.

Tailoring enzymatic loading capacity on CdS nanorods@ZnIn2S4 nanosheets 1D/2D heterojunctions: Toward ultrasensitive photoelectrochemical bioassay of tobramycin.

Despite advances in the development of photoelectrochemical (PEC) sensor, modulating the PEC response of assembled heterostructure interface is still a great challenge. Here, an ultrasensitive PEC aptasensor for tobramycin (TOB) assay was conducted based on one-dimensional/two-dimensional CdS nanorods@ZnIn2S4 nanosheets (1D/2D CdS NRs@ZnIn2S4 NSs) heterojunctions by tailoring enzymatic loading capacity. Firstly, alkaline phosphatase modified TOB aptamer (ALP-Apt) was linked via specific base complementary pairing, and insoluble precipitations were then produced through the ALP-triggered catalytic reaction with the aid of Ag+, which prevented the charge transfer and resulted in the decrement of photocurrent. In the presence of TOB, partial ALP-Apt detached from the electrode surface due to the strong affinity between TOB and its aptamer, leading to a reduction in the amount of ALP and insoluble precipitate, in turn the PEC response partially recovered. The photocurrents exhibited a wider linear range towards the TOB concentration of 1.0-5.0 × 104 pg mL-1, with a low detection limit of 0.96 pg mL-1. The constructed PEC aptasensor gained satisfactory results for TOB assay in milk samples as well, which also offered significant promise for other pollutants in environmental analysis.

Ultrasensitive photoelectrochemical aptasensor for detecting telomerase activity based on Ag2S/Ag decorated ZnIn2S4/C3N4 3D/2D Z-scheme heterostructures and amplified by Au/Cu2+-boron-nitride nanozyme.

Enzyme-mediated signal amplification strategies have gained substantial attention in photoelectrochemical (PEC) biosensing, while natural enzyme on the photoelectrode inevitably obstructs the interfacial electron transfer, in turn deteriorating the photocurrent responses. Herein, Au nanoparticles and Cu2+-modified boron nitride nanosheets (AuNPs/Cu2+-BNNS) behaved as nanozyme to achieve remarkable magnification in the PEC signals from a novel signal-off aptasensor for ultra-sensitive assay of telomerase (TE) activity based on Ag2S/Ag nanoparticles decorated ZnIn2S4/C3N4 Z-scheme heterostructures (termed as Ag2S/Ag/ZnIn2S4/C3N4, synthesized by hydrothermal treatment). Specifically, telomerase primer sequences (TS) were extended by TE in the presence of deoxyribonucleoside triphosphates (dNTPs), which was directly bond with the thiol modified complementary DNA (cDNA), achieving efficient linkage with the nanozyme via Au-S bond. The immobilized nanoenzyme catalyzed the oxidation between 4-chloro-1-naphthol (4-CN) and H2O2 to generate insoluble precipitation on the photo-electrode. By virtue of the inhibited PEC signals with the TE-enabled TS extension, an aptasensor for assay of TE activity was developed, showing the wide linear range of 50-5×105 cell mL-1 and a low detection limit of 19 cell mL-1. This work provides some valuable guidelines for developing advanced nanozyme-based PEC bioanalysis of diverse cancer cells.

Cu Nanoclusters-Encapsulated Liposomes: Toward Sensitive Liposomal Photoelectrochemical Immunoassay.

Herein we report the strategy of liposome-mediated Cu2+-induced exciton trapping upon CdS quantum dots (QDs) for amplified photoelectrochemical (PEC) bioanalysis application. Specifically, the Cu nanoclusters (NCs)-encapsulated liposomes were first fabricated and then processed with antibodies bound to their external surfaces. After the sandwich immunocomplexing, the confined liposomal labels were subjected to sequential lysis treatments for the release of Cu NCs and numerous Cu2+ ions, which were then directed to interact with the CdS QDs electrode. The interaction of Cu2+ ions with CdS QDs could generate CuxS and form the trapping sites to block the photocurrent generation. Since the photocurrent inhibition is closely related with the Cu NCs-loaded liposomal labels, a novel and general "signal-off" PEC immunoassay could thus be tailored with high sensitivity. Meanwhile, a complementary "signal-on" fluorescent detection could be accomplished by measuring the fluorescence intensity originated from the Cu NCs. This work features the first use of Cu NCs in PEC bioanalysis and also the first NCs-loaded liposomal PEC bioanalysis. More importantly, by using other specific ions/reagents-semiconductors interactions, this protocol could serve as a common basis for the general development of a new class of liposome-mediated PEC bioanalysis.