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.

This work developed a near-infrared (near-IR) light-activated non-enzymatic signal-off photoelectrochemical (PEC) immunoassay for the ultrasensitive detection of α-fetoprotein (AFP) on the basis of branched polyethylenimine (BPEI)-modified upconversion nanoparticle (UCNP)@CdTe quantum dot (QD) nanostructures by coupling with the synergistic effect of dual-purpose copper ions. Emission light originated from NaYF4:Yb,Er UCNP was directly utilized through the electrostatic bonding of CdTe QDs to excite the separation of electron–hole pairs, resulting in the generation of obvious photocurrent under a 980 nm laser. By using polyclonal antibody-labeled cupric oxide nanoparticle as the secondary antibody, the nanolabel was introduced into the monoclonal anti-AFP antibody-modified microplates in the presence of target AFP. After treatment with acid, the as-released copper ion decreased the photocurrent through the synergistic effect with two issues: one was initially to form coordination with BPEI on the surface of UCNP, and then the near-IR excitation light and upconversion luminescence were attenuated due to the internal filter effect; another was to snatch the electrons flowing from the valence band of CdTe QD as the exciton trapping sites. Under optimal conditions, the dual-purpose Cu2+-activated signal-off PEC immunosensing platform exhibited a dynamic linear range from 10 pg mL–1 to 50 ng mL–1, accompanying the decreasing photocurrent with the increment of AFP concentration at an experimental detection limit of 1.2 pg mL–1. Importantly, good accuracy was achieved by this method in comparison with the results with human AFP ELISA kit for analysis of human serum samples. This dual-purpose Cu2+-activated PEC immunoassay brings a promising, enzyme-free and innovative thinking for the detection of low-abundance biomarkers.

No abstract

A split-type photoelectrochemical immunoassay was designed to detect AFB1 in foodstuffs using amorphous TiO2 and CsPbBr3 perovskite nanocrystals.