This work presented an innovative and rationally engineered palindromic molecular beacon (PMB) based "Z-scheme" photoelectrochemical (PEC) biosensing protocol for the selective screening of kanamycin (Kana) through DNA hybridization-induced conformational conversion. Interestingly, the ingeniously designed PMB integrated the multifunctional elements including recognition region, primer-like palindromic fragment, and polymerization-nicking template. The cosensitized structures consisted of CdS quantum dot functionalized hairpin DNA2 (QD-HP2) and region-selectively deposited gold nanoparticles onto {001} facets of bismuth oxychloride (BiOCl-Au). Compared with BiOCl-Au alone, the attachment of CdS QDs onto BiOCl-Au (i.e., BiOCl-Au-CdS QDs) exhibited evidently enhanced photocurrent intensity thanks to the synergistic effect of Z-scheme BiOCl-Au-CdS QDs. After incubation with target Kana, Kana−aptamer binding could induce the exposure of PMB region for hairpin DNA1 (HP1). The exposed palindromic tails hybridized with each other (like a molecular machine) to consume the substrates (dNTPs) and fuels (enzyme) for the releasing of numerous nick fragments (Nick). The asgenerated nick fragments could specifically hybridize with the complementary region of QD-HP2, thus resulting in decreasing photocurrent because of the increasing spatial distance for electron transfer between two-type photosensitizers. Under optimum conditions, the PMB-based sensing system exhibited satisfying photocurrent responses toward target Kana within the working range from 50 to 5000 fM at a low detection limit of 29 fM. Impressively, the concept of a palindromic fragment-mediated primer-free biosensing strategy offers a new avenue for advanced development of efficient and convenient biodetection systems.
A novel photoelectrochemical (PEC) enzyme immunoassay was designed for the ultrasensitive detection of alpha-fetoprotein (AFP) based on near-infrared (NIR) light-excited core-core-shell UCNP@Au@CdS upconversion nanospheres. Plasmonic gold (Au) between the sandwiched layers was not only utilized as an energy harvester for the collection of the incident light but also acted as an energy conveyor to transfer the energy from upconversion NaYF:Yb,Er (UCNP) to semiconductor CdS, thus exciting the efficient separation of electron-hole pairs by the generated HO of enzyme immunoreaction under the irradiation of a 980 nm laser. By virtue of high catalytic activity of natural enzymes, gold nanoparticles heavily functionalized with glucose oxidase (GOx) and polyclonal anti-AFP antibody were utilized to generate HO. A sandwiched immunoreaction was first carried out in a monoclonal anti-AFP antibody-coated microplate by using an antibody-labeled gold nanoparticle as secondary antibody. Accompanying the gold nanoparticle, the carried GOx oxidized glucose in HO, thereby resulting in the enhanced photocurrent via capturing holes on the valence band of CdS to promote the separation of electron-hole pairs. Under optimum conditions, the NIR light-based PEC immunosensing system exhibited good photocurrent responses toward target AFP within the dynamic working range of 0.01-40 ng mL at a detection limit of 5.3 pg mL. Moreover, the NIR light-based sensing platform had good reproducibility and high selectivity. Importantly, good well-matched results obtained from NIR light-based PEC immunoassay were acquired for the analysis of human serum specimens by using AFP ELISA kit as the reference.
Pressure-based bioassays incorporating biomolecular recognition with a catalyzed gas-generation reaction have been developed for gas biosensors, but most involve poor sensitivity and are unsuitable for routine use. Herein we design an innovative gas pressure-based biosensing platform for the detection of Kanamycin (Kana) on polyaniline nanowires-functionalized reduced graphene oxide (PANI/rGO) framework by using platinum nanozyme-catalyzed gas generation. The signal was amplified by coupling with catalytic hairpin assembly (CHA) and strand-displacement amplification (SDA). Upon target Kana introduction, the analyte initially triggered a SDA reaction between hairpin DNA1 and hairpin DNA2, and then induced CHA conjugation between magnetic bead-labeled hairpin DNA3 (MB-H3) and platinum nanoparticle-labeled hairpin DNA4 (Pt-H4) to form a three-dimensional network. Numerous platinum nanoparticles (peroxidase-like nanozymes) were carried over with magnetic beads to reduce hydrogen peroxide into oxygen. The as-produced gas compressed PANI/rGO frameworks (modified to polyurethane sponge, used as the piezoelectric materials) in a homemade pressure-tight device, thus causing the increasing current of PANI/rGO sponge thanks to its deformation. The change in the current caused by the as-generated gas pressure was determined on an electrochemical workstation. Under optimum conditions, PANI/rGO sponge exhibited outstanding compressibility, stable signal-waveform output, fast response and recovery time (≈109 ms), and the current increased with the increasing Kana concentration within a dynamic working range of 0.2-50 pM at a detection limit of 0.063 pM. Good reproducibility, specificity, and acceptable precision were acquired for Kana analysis. In addition, the accuracy of this method was monitored to evaluate real milk samples with the well-matched results obtained by using the referenced Kana ELISA kit.
This work presented a point-of-care (POC) photoelectrochemical (PEC) biosensing for the detection of human papillomavirus-16 (HPV-16) on a portable electrochemical detection system by using CRISPR-Cas12a trans-cleaving the G-quadruplex for the biorecognition/amplification and a hollow In2O3–In2S3-modified screen-printed electrode (In2O3–In2S3/SPE) as the photoactive material. G-quadruplexes were capable of biocatalytic precipitation (H2O2-mediated 4-chloro-1-naphthol oxidation) on the In2O3–In2S3/SPE surface, resulting in a weakened photocurrent, but suffered from trans-cleavage when the CRISPR-Cas12a system specifically recognized the analyte. The photocurrent results could be directly observed with the card-sized electrochemical device via a smartphone, which displayed a high-value photocurrent for these positive samples, while a low-value photocurrent for the target-free samples. Such a system exhibited satisfying photocurrent responses toward HPV-16 within a wide working range from 5.0 to 5000 pM and allowed for detection of HPV-16 at a concentration as low as 1.2 pM. The proposed assay provided a smartphone signal readout to enable the rapid screening PEC determination of HPV-16 concentration without sophisticated instruments, thus meeting the requirements of remote areas and resource-limited settings. We envision that combining an efficient biometric PEC sensing platform with a wireless card-sized electrochemical device will enable high-throughput POC diagnostic analysis.
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