Medical tests are required to identify the cause of illness. Sometimes, simple test is carried out for daily health management. Simple, fast and sensitive detection of biomarker proteins, viruses, and target cells related to diseases is desired. Specific affinities between the target molecules and anchor molecules on the detection surface have been used for sensing. Unfortunately, there are a number of significant problems in the detection of such specific biomarkers in bio-samples, including (1) a low concentration of target molecules, (2) large noise from nonspecific binding or adsorption from the sample solution, (3) the difficulty of selecting and obtaining antibodies for the target molecule, and so on.
We have synthesized a new organic material modifing the sensing surfaces and have constructed a functional nanostructured monolayer surface that has demonstrated sufficiently high performance to detect low-concentration target marker molecules in the crude sample.
There are specific interactions between carbohydrates and proteins (lectins). However these interactions are quite weak. We have designed a lectin detection surface with carbohydrate-terminated alkanethiol and hydroxyl group (-OH)-terminated short alkanethiol on the substrate in order to improve lectin-carbohydrate binding and suppress nonspecific binding. Lectin-carbohydrate interaction on approximately 10-30 % carbohydrate mixed monolayers were compared with that on a 100 % carbohydrate monomolecular layer modified surface. The amount of lectin adsorption was increased and the interaction became stronger in the case of 10 % carbohydrate mixed monolayer.
We also investigated the resistance to nonspecific protein adsorption. We synthesized and used tri(ethylene glycol)-terminated alkanethiols as a protein-repelling modifier. These new molecules contribute to the affective suppression of noise and the highly effective detection of lectins(Fig.1)[1,3,4].
Our next project is the functionalization of other material surfaces for the construction of sensitive, effective, and simple detection interfaces for target molecules, in addition to present gold substrate. We are also making efforts to develop a new method and concept for the detection of disease marker molecules(Fig.2).