A plasmonic nanoledge array sensor for detection of anti-insulin antibodies of type 1 diabetes biomarker.

Here we present a plasmonic nanoledge device with high sensitivity and selectivity used to detect protein biomarkers simply by functionalizing the device, which specifically binds to particular biomolecule or biomarkers. We employ this plasmonic nanoledge device for the detection of anti-insulin antibodies of type 1 diabetes (T1D) in buffer and human serum at the range of pg ml-1 to 100 ng ml-1. The signal transduction is based on the extraordinary optical transmission (EOT) through the nanoledge array and the optical spectral changes with the biological binding reaction between the surface functionalized insulin with anti-insulin antibody. Control experiments indicate little interferences from the human serum background and addition of other proteins such as bovine serum albumin (BSA) and epidermal growth factor (EGF) at 20 ng ml-1. The high sensitivity, specificity and easy adaptability of the plasmonic device offer new opportunities in biosensing and diagnostic applications for T1D.

Plasmon-Enhanced Fluorescence of Carbon Nanodots in Gold Nanoslit Cavities.

Carbon nanodots (CNDs) are featured with a wide range of light absorption and excitation-dependent fluorescence. The emission enhancement of CNDs is of great interest for the development of nanophotonics. Although the phenomenon of plasmon-enhanced fluorescence for quantum dots and molecular dyes has been well investigated, rarely has it been reported for CNDs. In this work, a series of plasmonic nanoslit designs were fabricated and utilized for immobilization of CNDs in nanoslits and examination of the best match for plasmonic fluorescence enhancement of CNDs. In concert, to better understand the plasmonic effect on the enhancement, the surface optical field is measured with or without CND immobilization using a hyperspectral imaging system as a comparison, and a semianalytical model is conducted for a quantitative analysis of surface plasmon generation under the plane-wave illumination. Both the fluorescence and surface reflection light intensity enhancement are demonstrated as a function of nanoslit width and are maximized at the 100 nm nanoslit width. The analysis of surface plasmon-exciton coupling of CNDs in the nanoslit area suggests that the enhancement is primarily due to plasmonic light trapping for increased electromagnetic field and plasmon-induced resonance energy transfer. This study suggests that incorporating CNDs in the plasmonic nanoslits may provide a largely enhanced CND-based photoemission system for optical applications.

Magnetoreception of Photoactivated Cryptochrome 1 in Electrochemistry and Electron Transfer.

Cryptochromes are flavoproteins whose photochemistry is important for crucial functions associated with phototropism and circadian clocks. In this report, we, for the first time, observed a magnetic response of the cryptochrome 1 (CRY1) immobilized at a gold electrode with illumination of blue light. These results present the magnetic field-enhanced photoinduced electron transfer of CRY1 to the electrode by voltammetry, exhibiting magnetic responsive rate constant and electrical current changes. A mechanism of the electron transfer, which involves photoinduced radicals in the CRY, is sensitive to the weak magnetic field; and the long-lived free radical FAD•- is responsible for the detected electrochemical Faradaic current. As a photoreceptor, the finding of a 5.7% rate constant change in electron transfer corresponding to a 50 µT magnetic field may be meaningful in regulation of magnetic field signaling and circadian clock function under an electromagnetic field.

Plasmon-Exciton Coupling in Photosystem I Based Biohybrid Photoelectrochemical Cells.

The light-induced property of photosystem I (PSI) has been utilized to convert solar energy to electrical energy in photoelectrochemical cells. Here we provide new results on the relationship between surface plasmon generation (SPG) efficiency of nanoslits and the experimentally obtained photocurrent by immobilizing PSI on the gold nanoslit electrode surfaces regarding different nanoslit widths. The photocurrent increases with the increment of SPG efficiency. This finding can be attributed to the phenomenon of plasmon-exciton coupling effect on the PSI in the nanoslits. The enhancement of photocurrent generation is discussed on the basis of plasmonic light trapping and plasmon-induced resonance energy transfer.

A fluorescence-electrochemical study of carbon nanodots (CNDs) in bio- and photoelectronic applications and energy gap investigation.

Carbon nanodots (CNDs) have attracted great attention due to their superior solubility, biocompatibility, tunable photoluminescence, and opto-electronic properties. This work describes a new fluorescence-based spectroelectrochemistry approach to simultaneously study the photoluminescence and wavelength dependent photocurrent of microwave synthesized CNDs. The fluorescence of CNDs shows selective quenching upon a reversible redox couple, ferricyanide/ferrocyanide, reaction during cyclic voltammetry. The CND modified gold slide electrode demonstrates wavelength dependent photocurrent generation during the fluorescence-electrochemical study, suggesting the potential application of CNDs in photoelectronics. UV-Vis absorption and electrochemistry are used to quantify the energy gap of the CNDs, and then to calibrate a Hückel model for CNDs' electronic energy levels. The Hückel (or tight binding) model treatment of an individual CND as a molecule combines the conjugated π states (C[double bond, length as m-dash]C) with the functional groups (C[double bond, length as m-dash]O, C-O, and COOH) associated with the surface electronic states. This experimental and theoretical investigation of CNDs provides a new perspective on the optoelectronic properties of CNDs and should aid in their development for practical use in biomedicine, chemical sensing, and photoelectric devices.

Protein Trapping in Plasmonic Nanoslit and Nanoledge Cavities: The Behavior and Sensing.

A novel plasmonic nanoledge device was presented to explore the geometry-induced trapping of nanoscale biomolecules and examine a generation of surface plasmon resonance (SPR) for plasmonic sensing. To design an optimal plasmonic device, a semianalytical model was implemented for a quantitative analysis of SPR under plane-wave illumination and a finite-difference time-domain (FDTD) simulation was used to study the optical transmission and refractive index (RI) sensitivity. In addition, total internal reflection fluorescence (TIRF) imaging was used to visualize the migration of fluorescently labeled bovine serum albumin (BSA) into the nanoslits; and fluorescence correlation spectroscopy (FCS) was further used to investigate the diffusion of BSA in the nanoslits. Transmission SPR measurements of free prostate specific antigen (f-PSA), which is similar in size to BSA, were performed to validate the trapping of the molecules via specific binding reactions in the nanoledge cavities. The present study may facilitate further development of single nanomolecule detection and new nanomicrofluidic arrays for effective detection of multiple biomarkers in clinical biofluids.

Alternative SiO2 Surface Direct MDCK Epithelial Behavior.

The mechanical interactions of cells are mediated through adhesive interactions. In this study, we examined the growth, cellular behavior, and adhesion of MDCK epithelial cells on three different SiO2 substrates: amorphous glass coverslips and the silicon oxide layers that grow on ⟨111⟩ and ⟨100⟩ wafers. While compositionally all three substrates are almost similar, differences in surface energy result in dramatic differences in epithelial cell morphology, cell-cell adhesion, cell-substrate adhesion, actin organization, and extracellular matrix (ECM) protein expression. We also observe striking differences in ECM protein binding to the various substrates due to the hydrogen bond interactions. Our results demonstrate that MDCK cells have a robust response to differences in substrates that is not obviated by nanotopography or surface composition and that a cell's response may manifest through subtle differences in surface energies of the materials. This work strongly suggests that other properties of a material other than composition and topology should be considered when interpreting and controlling interactions of cells with a substrate, whether it is synthetic or natural.