Plasmonic nucleotide hybridization chip for attomolar detection: localized gold and tagged core/shell nanomaterials.

We report a large amplification of surface plasmon signals for a double hybridization microarray chip assembly that bridges localized gold and detection probe-carrying-core/shell Fe3O4@Au nanoparticles for detection of as low as 80 aM miRNA-155 marker in solution. The plasmonic wavelength match of the gold shell with surface localized gold nanoparticles and the additional scattering band of the core/shell material in resonance with the incident 800 nm light source are the underlying factors for the observed remarkable analyte signal at ultra-low (10-18 order) concentrations.

Measuring Ultra-low Levels of Nucleotide Biomarkers Using Quartz Crystal Microbalance and SPR Microarray Imaging Methods: A Comparative Analysis.

Circulating serum nucleotide biomarkers are useful indicators for early diagnosis of cancer, respiratory illnesses, and other deadly diseases. In this work, we compared detection performances of a quartz crystal microbalance (QCM), which is a mass sensor, with that of a surface plasmon resonance (SPR) microarray for an oligonucleotide mimic of a microRNA-21 biomarker. A surface immobilized capture oligonucleotide probe was used to hybridize with the target oligonucleotide (i.e., the microRNA-21 mimic) to facilitate selective detection. To obtain ultra-low femtomolar (fM) detection sensitivity, gold nanoparticles (50 nm) were conjugated with the target oligonucleotide. We achieved detection limits of 28and 47 fM for the target oligonucleotide by the QCM and SPRi microarray, respectively. We also conducted sample recovery studies and performed matrix effect analysis. Although the QCM had a lower detection limit, the microarray approach offered better throughput for analysis of up to 16 samples. We confirmed that the designed assay was selective for the target oligonucleotide and did not show signals for the control oligonucleotide with five mismatch sites relative to the target sequence. Combination of the QCM and microarray methods that utilize the same assay chemistry on gold are useful for overcoming clinical sample matrix effects and achieving ultra-low detection of small nucleotide biomarkers with quantitative insights.

Label-Free Real-Time Microarray Imaging of Cancer Protein-Protein Interactions and Their Inhibition by Small Molecules.

A rapid optical microarray imaging approach for anticancer drug screening at specific cancer protein-protein interface targets with binding kinetics and validation by a mass sensor is reported for the first time. Surface plasmon resonance imager (SPRi) demonstrated a 3.5-fold greater specificity for interactions between murine double minute 2 protein (MDM2) and wild-type p53 over a nonspecific p53 mutant in a real-time microfluidic analysis. Significant percentage reflectivity changes (Δ%R) in the SPRi signals and molecular-level mass changes were detected for both the MDM2-p53 interaction and its inhibition by a small-molecule Nutlin-3 drug analogue known for its anticancer property. We additionally demonstrate that synthetic, inexpensive binding domains of interacting cancer proteins are sufficient to screen anticancer drugs by an array-based SPRi technique with excellent specificity and sensitivity. This imaging array, combined with a mass sensor, can be used to study quantitatively any protein-protein interaction and screen for small molecules with binding and potency evaluations.

Surface plasmon resonance imaging of gold-small molecule interactions is influenced by refractive index and chemical structures.

HYPOTHESIS: We hypothesize that surface plasmon resonance imaging (SPRi) of interactions between small organic compounds and gold is influenced by the refractive index and chemical structures of the compounds. EXPERIMENTS: For the first time we imaged the SPR signals upon interaction of a gold surface with seven compounds representing aromatic, cyclic, short chain, and long chain carbon structures using an array format. FINDINGS: The refractive index and chemical structures of the tested compounds influenced the sensitivity of detection of the SPR microarray imager. Thus, the array methodology presented herein is suitable for studying interactions of small molecules with a gold surface.