Metal organic framework-derived CuO/Cu2O polyhedron-CdS quantum dots double Z-scheme heterostructure for cathodic photoelectrochemical detection of Hg2+ in food and environment.

This study employed an innovative copper oxide/cuprous oxide (CuO/Cu2O) polyhedron­cadmium sulphide quantum dots (CdS QDs) double Z-scheme heterostructure as a matrix for the cathodic PEC determination of mercury ions (Hg2+). First, the CuO/Cu2O polyhedral composite was prepared by calcining a copper-based metal organic framework (Cu-MOF). Subsequently, the amino-modified CuO/Cu2O was integrated with mercaptopropionic acid (MPA)-capped CdS QDs to form a CuO/Cu2O polyhedron-CdS QDs double Z-scheme heterostructure, producing a strong cathodic photocurrent. Importantly, this heterostructure exhibited a specifically reduced photocurrent for Hg2+ when using CdS QDs as Hg2+-recognition probe. This was attributed to the extreme destruction of the double Z-scheme heterostructure and the in situ formation of the CuO/Cu2O-CdS/HgS heterostructure. Besides, p-type HgS competed with the matrix for electron acceptors, further decreasing the photocurrent. Consequently, Hg2+ was sensitively assayed, with a low detection limit (0.11 pM). The as-prepared PEC sensor was also used to analyse Hg2+ in food and the environment.

Sensitive photoelectrochemical assay of Pb2+ based on DNAzyme-induced disassembly of the "Z-scheme" TiO2/Au/CdS QDs system.

Herein, based on DNAzyme-induced disassembly of the "Z-scheme" TiO2/Au/CdS QDs system, a facile and sensitive photoelectrochemical biosensor was developed for lead ion assay and a low detection limit of 0.13 pM was obtained.

A novel signal-off photoelectrochemical biosensor for M.SssI MTase activity assay based on GQDs@ZIF-8 polyhedra as signal quencher.

DNA methylation catalyzed by M.SssI methyltransferases (MTase) has important roles in gene expression and other cellular activities, and relates to some diseases, especially cancers. Therefore, it is important to develop a sensitive sensing platform for M.SssI MTase activity assay. Here, taking zeolitic imidazolate framework-8 (ZIF-8) polyhedra as the carriers of graphene quantum dots (GQDs), GQDs-embedded ZIF-8 polyhedra (denoted as GQDs@ZIF-8 polyhedra) were successfully prepared and used as the multi-functional signal quencher to construct a novel signal-off photoelectrochemical (PEC) biosensor for M.SssI MTase activity assay. Firstly, the indium tin oxide (ITO) slice was modified with TiO2, poly(diallyldimethylammonium chloride) and CdTe quantum dots (QDs). The obtained electrode was used as the photoelectrode and labeled as ITO/TiO2/CdTe QDs. Then, single-stranded DNA (S1) was anchored on the photoelectrode surface via S-Cd bond. After hybridization between S1 and biotinylated single-stranded DNA (S2), the streptavidin (SA)-labeled GQDs@ZIF-8 polyhedra were introduced to the modified electrode via the specific reaction between biotin and SA. As the signal quencher, GQDs@ZIF-8 polyhedra could not only inhibit the photocurrent signal of the ITO/TiO2/CdTe QDs electrode due to the steric hindrance effect, but also act as peroxidase mimetics to catalyze precipitation reaction of 4-chloro-1-naphthol, resulting in the evident depression of the photocurrent signal. For the specially designed S1/S2 double-strand DNA, the decreased photocurrent was quantitatively correlated with the M.SssI MTase activity (linear response range, 0.005-150 U mL-1; detection limit, 0.004 U mL-1). The developed GQDs@ZIF-8 polyhedra and related PEC biosensor may have potential applications in clinical research and disease diagnosis.

A sensitive photoelectrochemical methyltransferase activity assay based on a novel "Z-scheme" CdSe QD/afGQD heterojunction and multiple signal amplification strategies.

Here, based on a newly developed "Z-scheme" CdSe QD/afGQD heterojunction and multiple signal amplification strategies, a sensitive photoelectrochemical methyltransferase activity assay was carried out and a low detection limit of 0.046 U mL-1 was obtained.

A sensitive photoelectrochemical assay of miRNA-155 based on a CdSe QDs//NPC-ZnO polyhedra photocurrent-direction switching system and target-triggered strand displacement amplification strategy.

Herein, a new photoelectrochemical (PEC) biosensor based on a photocurrent direction switching system and target-triggered strand displacement amplification strategy was developed for the sensitive detection of microRNA (miRNA)-155, and it showed excellent selectivity and a low detection limit of about 49 aM.

Co3O4-Au Polyhedra: A Multifunctional Signal Amplifier for Sensitive Photoelectrochemical Assay.

Taking the zeolitic imidazolate framework (ZIF-67) as the precursor, p-type semiconducting Co3O4-Au polyhedra were synthesized and used as the signal amplifier to construct a sensitive photoelectrochemical (PEC) sensor for caspase-3 activity assay. Here, the n-type semiconductor Bi2S3-modified indium-tin oxide (ITO) slice was used as the photoelectrode. After immobilization of the biotin-DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Cys) onto the Bi2S3 surface, the streptavidin-labeled Co3O4-Au polyhedra were introduced to the sensing platform via the specific interaction between biotin and streptavidin. The Co3O4-Au polyhedra can not only quench the photocurrent of the Bi2S3 because of the competitive consumption of electron donors and exciting light energy (p-n-type semiconductor quenching effect), but also act as peroxidase mimetics to produce catalytic precipitate. Additionally, the steric hindrance effect from the Co3O4-Au polyhedra will decrease the PEC response of the Bi2S3. Ingeniously, the precipitates can not only deposit on the ITO electrode to decrease the photocurrent of PEC sensor, but also act as electron acceptors to scavenge the photogenerated electrons of Co3O4-Au polyhedra, leading to enhanced quenching ability of the Co3O4-Au polyhedra. When caspase-3 exists, caspase-3 can specifically recognize and cleave the biotin-DEVD-peptide, resulting in the increase of PEC response. Based on the multifunctional Co3O4-Au polyhedra, caspase-3 is detected sensitively with a linear range from 0.5 to 50 ng mL-1 and limit of detection down to 0.10 ng mL-1. The Co3O4-Au polyhedra provide a novel signal amplifier to construct PEC sensing platform and may have potential applications in bioanalysis, disease diagnostics, and clinical biomedicine.

A new photoelectrochemical biosensor for ultrasensitive determination of nucleic acids based on a three-stage cascade signal amplification strategy.

The sensitive and specific determination of nucleic acids is very important in clinical diagnosis and biological studies. In this work, an ultrasensitive photoelectrochemical (PEC) biosensor has been developed for DNA detection based on a "signal-on" sensing strategy and a three-stage cascade signal amplification method (catalytic hairpin assembly (CHA), hybridization chain reaction (HCR) and alkaline phosphatase (ALP)-triggered in situ generation of ascorbic acid (AA)). Here, CHA hairpin 1 (CHA-HP1) is opened by the target DNA (T-DNA) owing to the hybridization between T-DNA and CHA-HP1, and then the opened CHA-HP1 hybridizes with CHA hairpin 2 (CHA-HP2) to displace the T-DNA, generating a CHA-HP1/CHA-HP2 complex. The displaced T-DNA triggers the next cycle of CHA, resulting in the generation of numerous CHA-HP1/CHA-HP2 complexes. Subsequently, one end of the CHA-HP1/CHA-HP2 complex hybridizes with the capture DNA immobilized on the indium tin oxide/TiO2/CdS : Mn electrode. After the introduction of dual-biotin labeled HCR hairpin 1 (HCR-HP1-Bio) and dual-biotin labeled HCR hairpin 2 (HCR-HP2-Bio), the other end of the CHA-HP1/CHA-HP2 complex opens HCR-HP1-Bio. The opened HCR-HP1-Bio triggers the HCR reaction between HCR-HP1-Bio and HCR-HP2-Bio, leading to the formation of long nicked duplex DNA structures. The dual-biotin modified HCR-hairpins can anchor more streptavidin-ALP to catalyze 2-phospho-l-ascorbic acid trisodium salt to yield more AA, leading to a larger PEC response. The proposed PEC biosensor shows superior analytical performance for T-DNA detection with a linear response ranging from 0.1 fM to 100 pM and a detection limit of 0.052 fM, and may provide a powerful biosensing platform for bioanalysis and early disease diagnosis.

A label-free and blocker-free photoelectrochemical strategy for highly sensitive caspase-3 assay.

Herein, a new label-free and blocker-free photoelectrochemical (PEC) sensor based on bifunctional CC-DEVD-peptide modified nitrogen-doped porous carbon-ZnO nanopolyhedra/CdS hybrids is developed for highly sensitive caspase-3 assay. The developed PEC sensor shows a low detection limit of about 0.14 ng mL-1 and has promising applications in the apoptosis-associated study.