Abstract
In this study, a novel biosensor was developed based on high absorption and high scattering ability nanostructured materials to enhance the optical signal. Carbon nanotubes (CNTs) were used as a label material to demonstrate the feasibility for this approach. Human serum albumin (HSA) was selected as a detection target for its importance as a biomarker of liver function. The biosensor for HSA detection was characterized by ultraviolet-visible absorption spectroscopy (UV-Vis). The biosensor is composed of two components, a sensing-substrate and a CNT-label. The sensing-substrate is made of a piece of glass with the surface modified by bovine serum albumin (BSA) / anti-human serum albumin, monoclonal (AHSA) / 3-amicopropltriethoxysilane (APTES), to provide specific binding to HSA. The CNT-label is composed of CNTs which were immobilized with anti-human serum albumin, polyclonal (AHSA*) to label the detected HSA on the sensing substrate. AHSA* was covalently bound on CNTs with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) reaction to fabricate the CNT-label. The detection procedure of this biosensor was described as following. First, the sensing-substrate was immersed in HSA solution for the specific bonding of HSA on sensing-substrate. Second, the HSA-bonded sensing-substrate was immersed in a AHSA* modified CNT-label solution for the bonding of CNT-label with the detected HSA on the sensing-substrate (CNT-labeled sensing substrate). Finally, the optical transmission was measured by UV-Vis. The results show that there is a consistent reduction of transmission with increasing HSA concentrations. The reduction of the optical transmission is mainly contributed by CNTs bound on the substrates because of their high absorption coefficient and the high scattering ability. Moreover, the calibration results show good linearity between HSA concentration in log scale and reduction in optical transmission. The biosensor exhibits high sensitivity for the HSA detecting with a detection limit of 2.88 × 10−5 mg/ml. Compared with other nanomaterial-based immunoassay biosensors which also use UV-Vis for signal measuring, this biosensor exhibits lower detection limit (2.88 × 10−5 mg/ml) and wider detection range (0.43-3000 nM) than those using gold nanoparticle for antigen detection biosensors. Moreover, this approach provides an innovative mechanism to detect antigen. Above results demonstrate the feasibility of using nanostructured material with high absorption and high scattering ability as a label material for biosensors that can quantify antigen concentration, and provide high-sensitivity and wide detection range applications.