Comparison of photovoltaic behaviors for horseradish peroxidase and its mimicry by surface photovoltage spectroscopy

Abstract Surface photovoltage spectroscopy (SPS) was chosen to study the photovoltaic behavior of horseradish peroxidase (HRP), hemin and immobilized hemin (poly(NIPAAm/MBA/hemin)). Different photovoltaic behaviors were observed in these three systems. In air, similar SPS curves were found for HRP and poly(NIPAAm/MBA/hemin) with different response intensities. However, poly(NIPAAm/MBA/hemin) showed a wider changing range upon increasing the positive and negative bias to 1.0 V. The SPS of hemin showed a total different behavior when an external positive potential was applied. In vacuum, clearly different photovoltaic behaviors were found. Moreover, the response value decreased when HRP was exposed to O 2 , the SPS intensity was different from that in air, and could be altered by changing the external biases. On the other hand, the SPS could not be changed before and after poly(NIPAAm/MBA/hemin) was exposed to O 2 . These differences may result from different chemical microenvironments for hemin in HRP versus that in poly(NIPAAm/MBA/hemin). It could be concluded that H 2 O and O 2 were important factors affecting the photovoltage response in HRP, but only H 2 O played this important role in poly(NIPAAm/MBA/hemin).