Label-Free Highly Sensitive Detection of Proteins in Aqueous Solutions Using Surface-Enhanced Raman Scattering

We detected concentration-dependent surface-enhanced Raman scattering (SERS) spectra of several label-free proteins (lysozyme, ribonuclease B, avidin, catalase, and hemoglobin) for the first time in aqueous solutions. Acidified sulfate was used as an aggregation agent to induce high electromagnetic enhancement in SERS. Strong SERS spectra of simple and conjugated protein samples could easily be accessed after the pretreatment with the aggregation agent. The detection limits of the proposed method for lysozyme and catalase were as low as 5 μg/mL and 50 ng/mL, respectively. This detection protocol for label-free proteins has combined simplicity, sensitivity, and reproducibility and allows routine qualitative and relatively quantitative detections. Thus, it has great potential in practical high-throughput protein detections

Coomassie Brilliant Dyes as Surface-Enhanced Raman Scattering Probes for Protein−Ligand Recognitions

Coomassie brilliant dyes have high affinity to proteins and high Raman activity, and on the basis of which, we have employed brilliant blue R-250 (BBR) and brilliant blue G-250 (BBG) as surface-enhanced Raman scattering (SERS) labels to probe protein−ligand recognitions. This method differs from previously proposed methods in that target proteins are labeled rapidly before biological recognitions without procedures of separation and purification, rather than attaching Raman labels to metal nanoparticles, which significantly simplifies the Raman dye labeling procedure. In typical assays, ligand-functionalized metal nanoparticles assemble by target protein-specific bindings and this assembly sequentially turns on electromagnetic enhancement of Raman scattering of the proposed labels. The method with its advantages of rapidness, high sensitivity, and spectral multiplexing has great potential in probing protein−protein and protein−small molecule recognitions not only in solution systems but also on flexible solid substrates

Protein-Mediated Sandwich Strategy for Surface-Enhanced Raman Scattering: Application to Versatile Protein Detection

For surface-enhanced Raman scattering (SERS)-based protein identification, immunoassay, and drug screening, metal sandwich substrates bridged by proteins have been created in the present study. The sandwich architectures are fabricated based on a layer-by-layer (LbL) technique. The first gold monolayer is prepared by the self-assembling of gold nanoparticles on a poly(diallyldimethylammonium chloride) (PDDA)-coated glass slide. The second gold or silver layer is produced by the interactions between proteins in the middle layer of the sandwich architecture and the metal nanoparticles. Highly reproducible surface-enhanced resonance Raman scattering (SERRS) and SERS spectra can be obtained by the present gold-protein-gold (Au/Au) and gold-protein-silver (Au/Ag) sandwiches, and we find that the latter yields about 7 times stronger SERRS than the former. Because of contributions from the two metal layers to the SERS, this sandwich strategy holds great potential in highly sensitive and reproducible protein detections

Simplified Protocol for Detection of Protein−Ligand Interactions via Surface-Enhanced Resonance Raman Scattering and Surface-Enhanced Fluorescence

A simple and effective protocol for detections of protein−protein and protein−small molecule interactions has been developed. After interactions between proteins and their corresponding ligands, we employed colloidal silver staining for producing active substrates for surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). Tetramethylrhodamine isothiocyanate (TRITC) and Atto610 were used for both Raman and fluorescent probes. We detected interactions between human IgG and TRITC−anti-human IgG, and those between avidin and Atto610-biotin by surface-enhanced resonance Raman scattering (SERRS) and SEF. The detection limits of the proposed SERRS-based method are comparable to those of the proposed SEF-based one, 0.9 pg/mL for anti-human IgG and 0.1 pg/mL for biotin. This protocol exploits several advantages of simplicity over other SERS and SEF-based related methods because of the protein staining-based strategy for silver nanoparticle assembling, high sensitivity from SERRS and SEF, and high stability in photostability comparing to fluorescence-based protein detections. Therefore, the proposed method for detection of protein−ligand interactions has great potential in high-sensitivity and high-throughput chip-based protein function determination