A macroporous TiO2 film (M-TiO2 ), which was prepared by burning off the polystyrene microsphere (PS) template from a PS/TiO2 composite film, can provide a large active surface, improve electron-transport performance, and increase the photocurrent. Furthermore, core-shell-shell CdSeTe@CdS@ZnS quantum dots (QDs) were introduced to sensitize the M-TiO2 film, which can efficiently broaden the absorption spectra range, separate and transfer charge carriers, reduce recombination loss, and improve photovoltaic response, with a sensitization shell of CdS and a passivation shell of ZnS. A multisignal-amplified photoelectrochemical platform was fabricated by further modifying this film with a combination of biotin-DEVD-peptide (Biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) (which is specifically cleaved by caspase-3) and streptavidin-labeled alkaline phosphatase (SA-ALP). Under the enzymatic catalysis of ALP with the substrate 2-phospho-L-ascorbic acid trisodium salt (AAP), ascorbic acid (AA) was generated as a better electron donor, leading to increased photocurrent output. The activity of caspase-3, which depends on the amount of residual peptide on the electrode, was inversely proportional to the amount of AA. By monitoring the variation of photocurrent caused by AA, caspase-3 activity and the therapeutic effect of nilotinib (a special medicine of chronic myeloid leukemia, CML) were indirectly detected and evaluated. The photoelectrochemical platform can be used as a potential evaluation system for monitoring caspase-3 activity and drug effects.
Keywords: apoptosis; biosensors; microporous materials; quantum dots; semiconductors.
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