Detection of embryonic stem cell lysate biomarkers by surface plasmon resonance with reduced nonspecific adsorption.

Surface plasmon resonance imaging (SPRi) has emerged as a versatile biosensor to detect a wide range of biomolecular interactions with divergent potential applications. However, the use of this advanced-level technology for stem cell lysate study is still not much explored. Cell lysates are significant biological analytes used for disease diagnostics and proteomic studies, but their complex nature limits their use as an analyte for SPRi biosensors. Here, we review the problems associated with the use of SPRi for stem cell lysate study and examine the role of surface chemistry, running buffer, and blocking solution in order to minimize nonspecific adsorption (NSA). We detect the expression of Oct4, Sox2, Nanog, Rex1, and Lin28 biomarkers present in mouse embryonic stem cell (mESC) lysate against their corresponding antibodies immobilized on the sensor surface with reduced NSA. The current study shows that the conjunction of SPRi and microarray can be used as a label-free, high-throughput, and rapid technique for detection of biomarkers and their relative abundance in stem cell lysate study.

Predicting the right spacing between protein immobilization sites on self-assembled monolayers to optimize ligand binding.

Self-assembled monolayers designed to immobilize capture antibodies are usually prepared using a mixture of functional and inactive linkers. Here, using low molar ratios (1:1 to 1:100) of the two linkers resulted in loss of binding capability of the anti-EGFR (epidermal growth factor receptor) antibody nimotuzumab, as assessed by surface plasmon resonance imaging. We then developed a simple theoretical model to predict the optimal surface density of the functional linker, taking into account the antibody size and linker diameter. A high (1:1000) dilution of the functional linker yielded the best results. As an advantage, this approach does not require chemical modification of the protein.

In situ protein microarrays capable of real-time kinetics analysis based on surface plasmon resonance imaging.

In recent years, in situ protein synthesis microarray technologies have enabled protein microarrays to be created on demand just before they are needed. In this paper, we utilized the TUS-TER immobilization technology to allow label-free detection with real-time kinetics of protein-protein interactions using surface plasmon resonance imaging (SPRi). We constructed an expression-ready plasmid DNA with a C-terminal TUS fusion tag to directionally immobilize the in situ synthesized recombinant proteins onto the surface of the biosensor. The expression plasmid was immobilized on the polyethylene imine-modified gold surface, which was then coupled with a cell-free expression system on the flow cell of the SPRi instrument. The expressed TUS fusion proteins bind on the surface via the immobilized TER DNA sequence with high affinity (∼3-7×10(-13)M). The expression and immobilization of the recombinant in situ expressed proteins were confirmed by probing with specific antibodies. The present study shows a new low cost method for in situ protein expression microarrays that has the potential to study the kinetics of protein-protein interactions. These protein microarrays can be created on demand without the problems of stability associated with protein arrays used in the drug discovery and biomarker discovery fields.

Emerging technology of in situ cell free expression protein microarrays.

Recently, in situ protein microarrays have been developed for large scale analysis and high throughput studies of proteins. In situ protein microarrays produce proteins directly on the solid surface from pre-arrayed DNA or RNA. The advances in in situ protein microarrays are exemplified by the ease of cDNA cloning and cell free protein expression. These technologies can evaluate, validate and monitor protein in a cost effective manner and address the issue of a high quality protein supply to use in the array. Here we review the importance of recently employed methods: PISA (protein in situ array), DAPA (DNA array to protein array), NAPPA (nucleic acid programmable protein array) and TUSTER microarrays and the role of these methods in proteomics.