Xin R. Cheng

Au nanoparticle-modified DNA sensor based on simultaneous electrochemical impedance spectroscopy and localized surface plasmon resonance.

Electrochemical impedance spectroscopy (EIS) and localized surface plasmon resonance (LSPR) were performed on the same Au nanoparticle (AuNP)-modified indium tin oxide (ITO) coated glass surfaces. Cyclic voltammetry was applied to electrodeposit AuNPs on ITO surface directly. The surface plasmon band characterization of AuNPs was initially studied by controlling the electrodeposition conditions. It was found that the size of AuNP clusters was significantly affected by the applied potential and KCl concentration in solution. The dual-detection platform was applied to detect DNA hybridization related to a specific point mutation in apolipoprotein E gene (ApoE), which was related to the progression of Alzheimers disease. The preliminary results facilitate the development of a versatile biosensor that can be easily miniaturized and integrated into a high-throughput diagnostic device.

Disposable Immunochips for the Detection of Legionella pneumophila Using Electrochemical Impedance Spectroscopy

The rapid diagnosis of Legionellosis is crucial for the effective treatment of this disease. Currently, most clinical laboratories utilize rapid immunoassays that are sufficient for the detection of Legionella serogroup 1, but not other clinically relevant serogroups. In this report, the development of a disposable immunochip system is described in connection with electrochemical impedance spectroscopy and fluorescence microscopy. The immunochips were prepared by covalently immobilizing fluorophore-conjugated L. pneumophilaantibodies on Au chips. The analytical performance of the immunochips was optimized as a prescreening tool for L. pneumophila. The versatile immunochips described here can be easily adapted for the monitoring of all Legionella serogroups in clinical and environmental samples.

Oxidative Stress Effect of Dopamine on α-Synuclein: Electroanalysis of Solvent Interactions

The interaction of dopamine (DA) and α-synuclein (α-S) can lead to protein misfolding and neuronal death triggered by oxidative stress relevant to the progression of Parkinsons disease (PD). In this study, interfacial properties associated with DA-induced α-S aggregation under various solution conditions (i.e., pH, ionic strength) were investigated in vitro. The electrochemical oxidation of tyrosine (Tyr) residues in α-S was detected in the presence of DA. DA concentration dependence was analyzed and found to significantly affect α-S aggregation pathways. At low pH, DA was shown to be stable and produced no observable difference in interfacial properties. Between pH 7 and 11, DA promoted α-S aggregation. Significant differences in oxidation current signals in response to high pH and ionic strength suggested the importance of initial interactions in the stabilization of toxic oligomeric structures and subsequent off-pathways of α-S. Our results demonstrate the importance of solution interactions with α-S and the unique information that electrochemical techniques can provide for the investigation of α-S aggregation at early stages, an important step toward the development of future PD therapeutics.

Au Nanostructured Surfaces for Electrochemical and Localized Surface Plasmon Resonance-Based Monitoring of α-Synuclein–Small Molecule Interactions

In this proof-of-concept study, the fabrication of novel Au nanostructured indium tin oxide (Au-ITO) surfaces is described for the development of a dual-detection platform with electrochemical and localized surface plasmon resonance (LSPR)-based biosensing capabilities. Nanosphere lithography (NSL) was applied to fabricate Au-ITO surfaces. Oligomers of α-synuclein (αS) were covalently immobilized to determine the electrochemical and LSPR characteristics of the protein. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed using the redox probe [Fe(CN)6](3-/4-) to detect the binding of Cu(II) ions and (-)-epigallocatechin-3-gallate (EGCG) to αS on the Au-ITO surface. Electrochemical and LSPR data were complemented by Thioflavin-T (ThT) fluorescence, surface plasmon resonance imaging (SPRi), and transmission electron microscopy (TEM) studies. EGCG was shown to induce the formation of amorphous aggregates that decreased the electrochemical signals. However, the binding of EGCG with αS increased the LSPR absorption band with a bathochromic shift of 10-15 nm. The binding of Cu(II) to αS enhanced the DPV peak current intensity. NSL fabricated Au-ITO surfaces provide a promising dual-detection platform to monitor the interaction of small molecules with proteins using electrochemistry and LSPR.

Optical trapping for the characterization of amyloid-beta aggregation kinetics

Alzheimers disease (AD) is marked by the accumulation of neuronal plaques from insoluble amyloid-beta (Aβ) peptides. Growing evidence for the role of Aβ oligomers in neuronal cell cytotoxicity and pathogenesis has prompted the development of novel techniques to better understand the early stages of aggregation. Near infrared (NIR) optical trapping was applied to characterize the early stages of Aβ aggregation in the presence of a β-sheet intercalating dye, Congo Red (CR), as the fluorescent marker. The integration of fluorescence analysis with NIR optical trapping has provided a new outlook into the first two hours of Aβ aggregation.

Photonic crystals on copolymer film for label-free detection of DNA hybridization

The presence of a single-nucleotide polymorphism in Apolipoprotein E4 gene is implicated with the increased risk of developing Alzheimers disease (AD). In this study, detection of AD-related DNA oligonucleotide sequence associated with Apolipoprotein E4 gene sequence was achieved using localized-surface plasmon resonance (LSPR) on 2D-Photonic crystal (2D-PC) and Au-coated 2D-PC surfaces. 2D-PC surfaces were fabricated on a flexible copolymer film using nano-imprint lithography (NIL). The film surface was then coated with a dual-functionalized polymer to react with surface immobilized DNA probe. DNA hybridization was detected by monitoring the optical responses of either a Fresnel decrease in reflectance on 2D-PC surfaces or an increase in LSPR on Au-coated 2D-PC surfaces. The change in response due to DNA hybridization on the modified surfaces was also investigated using mismatched and non-complementary oligonucleotides sequences. The proof-of-concept results are promising towards the development of 2D-PC on copolymer film surfaces as miniaturized and wearable biosensors for various diagnostic and defense applications.