ABSTRACT
Heretofore, the concept, principle, device, and system of the nano-imprint biosensor have been mainly described. The experimental results and application examples of the nanoimprint biosensor are presented in this chapter. 6.1 Detection of a-FetoproteinUsing the nanoimprint biosensor based on surface plasmon reso-nance (SPR) principle, we performed the quantitative detection of a-fetoprotein (AFP), a tumor marker. Although the AFP concentra-tion in healthy human serum is approximately 20 ng/mL, its level increases markedly to more than several hundred ng/mL in pa-tients with liver cancer (Teramura and Iwata, 2007). Currently, the cutoff value of AFP for clinical diagnosis is 200 ng/mL. Hence, the sensitive detection of the AFP using this system can be useful in cancer diagnosis. 6.1.1 Preparation of Probe LayerTo realize a high-sensitivity detection, the preparation of the probe layer is significant. Especially in nanoimprint biosensor, the thick-ness of the probe layer also needs to be taken into consideration. In this part, its preparation is presented. The experiment is conducted with the first proto-model which is introduced in Chapter 5.
For an SPR biosensing with nanoimprinted sensor device, the thickness of the probe layer to capture the target molecule should be smaller than 20 nm as the sensing depth is about 40-80 nm. To accomplish this purpose, we attempted to introduce an antibody-immobilization layer using ORLA18 protein (Orla Protein Technologies, UK). This ORLA18 protein is designed to present precisely oriented antibody (IgG)-binding domain structure as single layers (thickness ~10 nm) on surfaces (Athey et al., 2005). Its surface preparation process on the sensor device is explained below and depicted in Fig. 6.1. (1) Treatment of the gold surface on nanoimprinting sensor device by injecting an aqueous solution containing 1% (v/v),
