I am making a medical device that requires to sense very very low intensity blue light. I have attached my circuit design which is a 2-stage amplifier(transimpedance and differential amplifier), but I still need to increase the total gain of the circuit. Can someone please tell me how should I make modifications to my design to have a much higher gain. Should I add another 2-stage voltage amplifier?
Currently in my circuit (from the diagram), Rf=1Mohm, R2=1Mohm. If I increase these values, my dark voltage increases, which I do not want. It should give zero in dark which I am getting with these values. Photodiode being used is hamamtsu S1133 and opamp being used is TI OPA2381