A label-free optical immunoassay based on birefringence of liquid crystal for insulin-like growth factor-I sensing

Abstract

Human insulin-like growth factor-I (IGF-I) is a pleiotropic polypeptide hormone, which has been widely utilized for the diagnosis and management of growth hormone (GH) related disorders and diseases. In this work, we verify a label-free optical biosensor based on nematic liquid crystals (LCs) of 4-cyano-4-pentylbiphenyl (5CB) for ultrasensitive sensing of trace IGF-I in human serum samples. 5CB shows unique birefringence driven by the reorientation of the self-assembled N, N-dimethyl-N-(3-(trimethoxysilyl)propyl)−1-octadecanaminiuchloride (DMOAP) on glass. IGF-I antibody (AbIGF-I), as a specific recognition element, can be immobilized onto modified glass surface through a cross-linker of glutaradehyde (GA) and (3-aminopropyl) trimethoxysilane (APTES). Based on the number of specific recognition and binding between antibody (AbIGF-1) and antigen (AgIGF-1), the LC film exhibits gradual change from dark to bright under crossed polarizer. Under optimized conditions, the constructed LC-based biosensor demonstrates high sensitivity to IGF-I with a detection limit (LOD) of 1.0 ng/mL and a linear range of 10.0–2000.0 ng/mL (R2 = 0.989). This detection method possesses the advantages of easy construction, rapid sensing, good stability and repeatability, and high specificity for distinguishing IGF-I from other interfering proteins. Meanwhile, the format of biosensor could quickly detect IGF-I within a physiological range, providing profound information for prevention and treatment of GH-IGF-I axis related diseases in clinical diagnosis.