A valuable visual colorimetric and electrochemical biosensor for porphyrin

Porphyrin is able to specifically combine with phosphorus, thus a novel bifunctional sensing platform for determination of porphyrin by visual colorimetry and electrochemistry was demonstrated. A pretreated gold sheet (or electrode) with 2-mercatpoethanol (2-ME) was chemically modified by POCl ₃ to obtain the surface phosphate active sites. The different stages of modified electrode were characterized by electrochemical impedance spectroscopy (EIS). The 1:1 cationic sitting-atop (SAT) complex P(V)-porphyrin was formed due to the high affinity of the modified gold sheet (or electrode) towards the porphyrin, resulting in electron transfer resistance increase of the electrode surface. Meanwhile, a dramatic color changing from burgundy to dark green of porphyrin solution was observed with the naked-eye within 3s. What's more, this was reflected by the notable change of the Soret band of porphyrin when using UV-vis. Two sensing systems provide different sensitivity for porphyrin analysis. With visual colorimetry, porphyrin can be detected at a level of 1.0×10 ^-6M, whereas the detection limit of porphyrin is 3.0×10 ^-8M using the EIS method. The practical application of the sensor to determination of pheophytin which was obtained from fresh spinach leaves has been accomplished. The results demonstrate the facility and effectivity of our introduced bifunctional biosensor for quantitative analysis of porphyrin.