short pulse amplifier

I have an application to detect flames using ionisation probes. Probes are constructed of a stainless steel coaxial cable. It is then biased with 80Vdc and as the flame reach the probe, I can achieve a pulse due to micro amp level current flow in the circuit (conduction occur through coaxial cable due to ions in flame). Following is the circuit that I am using at the moment which works fine for just one probe. However as I need 12 such probes and use a common supply, I observe cross talk between them.

So, I think I need to change my amplification circuit. The output of the amplifier triggers a digital input of an FPGA to log data in PC. therefore I need the amplifier designed to produce a TTL pulse as it detects the micro amp level current flow in the ionisation probe circuit.

I have used open loop configuration to achieve the maximum gain.

Really appreciate if you can advise me on this - particularly to design the amplification circuit.

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