Transimpedance amplifier bandwidth
Let's assume you want a reasonable response from the TIA, say 1 Volt.  For 0.8 uA signal that gives you a feedback resistor of 1.25 M\$\Omega\$.

Using \$F_p=\sqrt{\frac{GBW}{2{\Pi}{R_f}{C_D}}} \$ you see you need a high GBW to be able to get a high frequency response.

With your 2 Hz requirement your GBW of the opamp need only be ~ 1600 KHz.