We report on a CMOS RF transceiver designed for detection of biological objects such as cancer marker proteins. Its main function is to manipulate and monitor RF dynamics of protons in water via nuclear magnetic resonance (NMR). Target objects alter the proton dynamics, which is the basis for our biosensing. The RF transceiver has a measured receiver noise figure of 0.7 dB. This high sensitivity enabled construction of an entire NMR system around the RF transceiver in a 2-kg portable platform, which is 60 times lighter, 40 times smaller, yet 60 times more mass sensitive than a state-of-the-art commercial benchtop system. Sensing 20 fmol and 1.4 ng of avidin (protein) in a 5 muL sample volume, our system represents a circuit designer’s approach to pursue low-cost diagnostics in a portable platform.