Label-free measurements on the solution of monomeric and dimeric insulin using a periodical terahertz split ring resonator

A silicon-based sensor, consisting of periodical split ring resonators was demonstrated to monitor monomeric and dimeric insulin solutions in terahertz time-domain spectroscopy (THz-TDS). As concentration increases, the resonant frequencies of sensor show red shifts with a rapid trend in dilute solutions and a slow trend in concentrated solutions, consistent with CST simulations. For monomeric insulin, the turning concentration is 11.6 mg/ml and the total frequency shift is larger than that of dimeric insulin which shows a turning concentration at 17.4 mg/ml. The deviation in frequency shift and turning concentration can be attributed to the structural changes of insulin during dimerization process.