As a well-known copper-containing oxidase, tyrosinase has been anticipated to serve as the biomarker of skin diseases. We describe here an exquisite label-free fluorescent and colorimetric dual-readout assay of its activity, inspired by the specific oxidation ability of monophenolamine substrates to catecholamines and a unique fluorogenic reaction between resorcinol and catecholamines. By employing commercially available tyramine as the model substrate (dopamine as the product), it is found that the tyrosinase-incubated tyramine solution exhibits obvious pale yellow with intense blue fluorescence in the presence of resorcinol and O, where the absorbance and fluorescence intensity are directly related to the concentration of added tyrosinase (i.e., the amount of conversion of tyramine to dopamine). The overall process of sensing tyrosinase activity takes less than 100 min at ambient temperature and pressure conditions with exceedingly simple operation procedure, explicit response mechanism, and formation of fluorophore with high quantum yield from scratch. Furthermore, such a convenient, rapid, cost-effective, and highly sensitive dual-readout assay exhibits promising prospect for the tyrosinase activity in extensive bioassays and clinic research as well as in screening potential tyrosinase inhibitors.
Alkaline
phosphatase (ALP) usually acts as a signal transmitter
in enzyme-linked immunosorbent assay (ELISA); therefore, developing
an attractive ALP activity assay, especially using a preferable substrate,
would help improve the efficiency and convenience of ELISA in practical
applications. Herein we have first prepared an original and creative
substrate, named m-hydroxyphenyl phosphate sodium
salt (m-HPP), with a desirable dephosphorylation
site for ALP. On the basis of the ALP-catalyzed hydrolysis of m-HPP to resorcinol and its subsequent specific nucleophilic
reaction with dopamine, we have exploited a fluorometric and colorimetric
dual-readout ALP activity assay and ALP-based ELISA system. Under
the employed experimental conditions, highly sensitive and specific
assay of ALP and cardiac troponin I (cTnI) has been accomplished in
a straightforward way. Furthermore, the commendable sensing performance
of our proposed ELISA in the determination of the cTnI level in diluted
human serum unambiguously illustrates great potential in the early
diagnosis of acute myocardial infarction.
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