Highly Selective Photoelectrochemical Assay of Arsenate Based on Magnetic Co₃O₄–Fe₃O₄ Cubes and the Negative-Background Signal Strategy

Abstract

Water pollution presents a significant environmental concern on earth. Herein, due to the serious environmental harmfulness of arsenate [As(V)], an iron phthalocyanine (FePc)induced switchable photocurrent-polarity platform was developed for highly selective assay of As(V). First, magnetic Co 3 O 4 −Fe 3 O 4 cubes were obtained by calcination of the CoFe Prussian blue analogue and then functionalized with oligonucleotide (S1). In the presence of As(V), S1 could be released based on the stronger affinity between As(V) and Co 3 O 4 −Fe 3 O 4 cubes. After magnetic separation by Co 3 O 4 −Fe 3 O 4 cubes, the released S1 was used to trigger the catalytic hairpin assembly (CHA) and hybridization chain reaction, resulting in the formation of lots of G-quadruplex structures on the AgInS 2 /ITO electrode. Then, the capture of FePc by the G-quadruplex led to the switch of the photocurrent polarity of the AgInS 2 /ITO electrode from the anode to the cathode. Thus, As(V) was sensitively assayed with a low detection limit of 1.0 nM and a wide linear response range from 10 nM to 200 μM. This meets the detection requirement of the World Health Organization for the arsenic concentration in drinking water [less than 10 μg L −1 (130 nM)]. In addition, whether it was cationic or anionic interferents except phosphate (PO 4 3− ), only As(V) could generate the cathodic photocurrent, effectively avoiding the false-positive or false-negative results during As(V) assay. Interestingly, As(V) was also simultaneously separated from the detection system by Co 3 O 4 −Fe 3 O 4 magnetic cubes. The proposed photoelectrochemical platform may have a great potential application for the selective detection of As(V) in environmental fields.

Colorimetric and Photocurrent-Polarity-Switching Photoelectrochemical Dual-Mode Sensing Platform for Highly Selective Detection of Mercury Ions Based on the Split G-Quadruplex–Hemin Complex

“…The peaks at 779.8 and 794.8 eV suggest the existence of Co(III). 25 In addition, the XPS peaks of Si 2p at 103.1 eV (Figure 2D) and O 1s at 532.4 eV (Figure 2E) represent the presence of SiO 2 , 47 which is consistent with the XRD and TEM results. The peak at 533.1 eV in Figure 2E illustrates the presence of metal oxygen bonds (Co−O or Ni− O).…”

“…In order to overcome these shortcomings, several methods with low cost including colorimetric, electrochemical, and photoelectrochemical (PEC) techniques were developed for the detection of Hg 2+ . − Thereinto, PEC method has received much attention with many advantages including low background signal, easy operation, miniaturization, and so forth. − However, the current PEC methods for detecting mercury ions are still limited because many excellent photoactive materials (such as CoSx@CdS, ZnS@Ag 2 S, CdS, etc − which results in false-negative or false-positive results. In the last few years, the photocurrent-polarity-switching strategy was developed as a highly selective way to effectively avoid the false-negative or false-positive signals, , implying that a new sensing platform based on the photocurrent-polarity-switching strategy may be constructed for the selective assay of Hg 2+ .…”

Molecular Imprinted Poly(2,5-benzimidazole)-Modified VO2–CuWO4 Homotype Heterojunction for Photoelectrochemical Dopamine Sensing

“…Dopamine (DA) as a critical neurotransmitter plays an important role in normal human life and controls the metabolism and functioning of the central nervous, renal, and hormone systems. − Abnormal (low) levels of DA can cause neurological disorders such as hypertension, schizophrenia, Parkinson’s, Alzheimer’s, HIV, and attention-deficit hyperactivity disorder, while high DA levels can make people addicted. − Thus, there is an urgent demand to develop a robust, rapid, sensitive, and selective strategy for DA monitoring for disease prevention and treatment. Various analytical and bioanalytical methods, including colorimetric method, surface plasmon resonance, ion-exchange chromatography, fluorescence, high-performance liquid chromatography, chemiluminescence, electrochemiluminescence, and electrochemical method, have been developed to monitor DA in different media. ,− High signal background (low sensitivity) and bulky instruments are significant challenges in these methods. , Alternatively, increasing efforts have been focused on photoelectrochemical (PEC) assays as an attractive frontier in state-of-the-art analysis because of their advantages, such as low background signals and separation of excitation and detection signals. − PEC sensors are consisting of photoelectrically active support such as functional semiconductors (SCs) and quantum dots, as well as recognition agents such as aptamer, antibodies, protein, and so on. − Considering the inherent disadvantages of antibodies and aptamers such as low stability, high cost, photoelectric inactivity, and complex operation, developing novel recognition agents are very vital. − In addition, the strong oxidizability of OH radicals generated in PEC oxidation causes photocorrosion and severe reduction of selectivity. , Therefore, for designing a robust PEC sensor, the selection of a stable, biocompatible, photoelectrically active, and cost-effective recognition element of high electron mobility, excellent chemical and thermal stability, and photoelectrically active support is of high importance …”

Bifunctional Magnetic Fe3O4@Cu2O@TiO2 Nanosphere-Mediated Dual-Mode Assay of PTP1B Activity Based on Photocurrent Polarity Switching and Nanozyme-Engineered Biocatalytic Precipitation Strategies

“…What’s more, either the “signal-off” or “signal-on” strategy cannot avoid the false-positive or false-negative signals in practical applications due to the fact that various nonredox and redox interferents coexisting in samples will result in a decrease or an increase of the photocurrent. Recently, a photocurrent–polarity–switching strategy, that is, only the target would induce the switch of photocurrent polarity and the interferents could not switch the photocurrent polarity, was proposed in our group and found great advantages in avoiding the false-positive or false-negative results. , This inspires us to develop a new photocurrent–polarity–switching system for protein phosphatase activity assay based on the specific dephosphorylation process of phosphopeptide (P-peptide) by protein phosphatase.…”