In this paper we propose a novel high-resolution chemical sensing front-end with integrated sigma delta quantisation, and the chemical sensing capability is realised by the intrinsic passivation layer. A charge transfer amplifier with adjustable pre-amplification has been adopted to not only transmit the chemical signal to the next sampling stage, but also alleviate the kT/C thermal noise requirement. A pseudo-resistor is added to provide the DC operating points for the front-end, and it is implemented via a MOS transistor applying direct tunnelling effect to achieve huge resistance value. Simulation results show that through oversampling and noise shaping functions, the final resolution can reach up to 90.1 dB even with a 0.3V input signal, making it suitable for applications requiring high-precision chemical detection.