Linearity improvement of Cy5 fluorescence concentration detection using series photodetector frequency circuit system with ITO–PolySi–metal–semiconductor–metal photodetector and its application for DNA detection and bacterial identification

In this study, the 48 MHz series photodetector frequency circuit system with ITO–PolySi–metal–semiconductor–metal photodetector was developed for Cy5 fluorescence detection of DNA probe ET996. The theory analysis of series photodetector frequency circuit system showed that the circuit parameters such as Cp and A (tan θ) can be applied to improve the frequency sensitivity. In this research, the lower capacitance of ITO–PolySi–metal–semiconductor–metal photodetector (Cp) was made and selected to improve the frequency sensitivity. According to derived theory of A adjustment, the capacitance match Cm and bias of ITO–PolySi–metal–semiconductor–metal photodetector were adjusted to improve the frequency sensitivity for detection of fluorescence dye concentration. On the basis of optimal conditions of capacitance match Cm and bias of photodetector, the detection limit of ET996-Cy5 fluorescence dye concentration 2 pmol/L can be measured by 48 MHz sensor system. Moreover, the detection linearity of 48 MHz sensor system was improved and the frequency shift ΔF was linearly related to the logarithm of fluorescence dye concentration in the range 2 pmol/L–20 μmol/L; meanwhile, through the feature of probe uniqueness, Edwardsiella BCRC 10670 DNA and fluorescence probe ET996-Cy5 can be successfully judged for hybridization reaction.