Peroxidase-like and fluorescent activity of Ag nanozyme activated from polyvalent Mn engineering for multi-signal catalytic recognition of dopamine and ascorbic acid

To strengthen nano Ag peroxidase-like and fluorescent activity, a kind of polyvalent MnOx activated Ag-based bionic nanozyme (mMn-Ag QDs) was developed in this work. mMn-Ag QDs exhibited superior peroxidase-like and fluorescent activity to single nano Ag by virtue of the multi-valence engineering of Mn0, Mn2+, Mn3+, and Mn4+. Trace dopamine (DA) or ascorbic acid (AA), the requisite monitoring indicators for some diseases, could selectively alter the peroxidase-like or fluorescent activity with obvious hypochromic and “turn-on” fluorescent effects. Under optimized conditions, the detection limits were 3.62 × 10−8 M, 1.34 × 10−7 M, and 4.69 × 10−9 M for UV–vis, red-green-blue (RGB), and fluorescent tracking of DA, and the ones were 1.16 × 10−8 M and 6.84 × 10−8 M for UV–vis and RGB recognition of AA in real samples. The results also showed that DA contents in human urine were quite different during various periods in a day. The multi-signal analyses were reliably confirmed from F/t values. The mechanisms for synergistic-enhancement activity of mMn-Ag QDs and for selective recognition of DA and AA were proposed.