This paper presents a low-noise gain-tunable biopotential amplifier that is designed based on a foldedcascode structure. Sub-threshold and self-biasing techniques are employed to achieve a low-noise and low-power amplification. With a bias-current tuning block, the gain of the proposed biopotential amplifier can be precisely adjusted. Designed in a standard 0.13 lm CMOS process, the proposed amplifier provides a 5.9 kHz bandwidth and 30.1 dB gain with 732 nW power. The input-referred noise over the entire bandwidth is 4.3 μV rms, equivalent to a noise-efficiency factor of 2.48. © Springer Science+Business Media, LLC 2012.