Photonic crystal enhanced fluorescence emission and blinking suppression for single quantum dot digital resolution biosensing

Abstract

While nanoscale quantum emitters are effective tags for measuring biomolecular interactions, their utilities for applications that demand single-unit observations are limited by the requirements for large numerical aperture (NA) objectives, fluorescence intermittency, and poor photon collection efficiency resulted from omnidirectional emission. Here, we report a nearly 3000-fold signal enhancement achieved through multiplicative effects of enhanced excitation, highly directional extraction, quantum efficiency improvement, and blinking suppression through a photonic crystal (PC) surface. The approach achieves single quantum dot (QD) sensitivity with high signal-to-noise ratio, even when using a low-NA lens and an inexpensive optical setup. The blinking suppression capability of the PC improves the QDs on-time from 15% to 85% ameliorating signal intermittency. We developed an assay for cancer-associated miRNA biomarkers with single-molecule resolution, single-base mutation selectivity, and 10-attomolar detection limit. Additionally, we observed differential surface motion trajectories of QDs when their surface attachment stringency is altered by changing a single base in a cancer-specific miRNA sequence.

Sericin-Based Bio-Inspired Nano-Engineering of Heterometallic AgAu Nanocubes for Attomolar Mefenamic Acid Sensing in the Mobile Phone-Based Surface Plasmon-Coupled Interface

“…A metal ion solution (Ag + , Au 3+ , Ag + + Au 3+ ) was mixed with 1 wt % solution of SER protein solution in a 1:1 ratio and exposed to UV light. At definite time intervals (1,5,10,20,30, and 40 min), samples were pipetted out and immediately stored in the dark, in aluminum foilwrapped plastic vials, in order to prevent any interaction of samples with stray light. Using this frugal and simple one-pot synthesis, NPs of varied morphology were obtained.…”

“…In order to improve the performance of conventional fluorescence-based detection techniques, plasmonic/metallic nanoparticles (NPs) with novel optical functionalities are being progressively researched. , The fluorescence excitation and emission of a radiating dipole is significantly altered in the immediate vicinity of a plasmonic nanostructure. , Due to the high electric field intensity (on account of a high effective extinction coefficient) generated in the near field by plasmonic NPs, the fluorescence intensity undergoes drastic modifications. − Additionally, the excited fluorophores interact with the oscillating charge densities on metal NPs to generate plasmons that eventually radiate into observable far-field radiation. Consequently, the hybrid metal-fluorophore system is being addressed as a plasmophore (plasmon + fluorophore) as the far-field emission carries with it the characteristics of the emission from both of them. ,− Moreover, this strategy aids in obtaining an increased radiative decay rate, photostability, and decreased lifetimes resulting in a concomitant increase in the overall quantum yield. Hence, the studies based on metal-fluorophore ensembles have effectively developed into a mature field termed metal-enhanced fluorescence (MEF) that overcomes the limitations (low sensitivity) of traditional fluorescence spectroscopy. , …”

“…In spite of the new generation of nanoscale-based MEF sensor technologies, certain challenges remain as significant drawbacks with regard to low signal collection efficiency, high background noise, and poor spectral resolution. − Nevertheless, recent scientific advances in optical instrumentation have presented opportunities in overcoming the abovementioned caveats with the utility of metallic thin films in Kretschmann and reverse Kretschmann (RK) configurations. ,, The surface plasmon polaritons (SPPs) are generated upon light illumination at an appropriate angle so as to satisfy the phase-matching conditions at the metal–dielectric interface . The effective coupling between the metallic thin film and the dielectric nanolayer doped with fluorophores results in a highly directional and polarized emission with >50% signal collection efficiency, high spectral resolution, and background suppression.…”

Solvent-Responsive Invisible Photonic Patterns with High Contrast for Fluorescence Emission Regulation and Anti-Counterfeiting

“…On the other hand, it has been demonstrated that PCs can regulate the fluorescence emission of fluorophores by PBG, which can accurately manipulate the propagation of light with a specific wavelength by reducing the group velocity of light propagation and redistributing the density of optical states. − The local density of optical states and electromagnetic environments at different locations of PCs are different. Fluorescence emission is significantly suppressed and redistributed within PCs when the PBG of PCs overlaps with the fluorescence emission peak of the fluorophore since Bragg’s reflection inhibits light propagation. − Therefore, such IPPs with opposite responsiveness might have a significant regulatory effect on the embedded fluorophore, bringing the dual-display mode of the structural color pattern and fluorescence pattern with high contrast.…”

Photonic-Plasmonic Coupling Enhanced Fluorescence Enabling Digital-Resolution Ultrasensitive Protein Detection

“…While these approaches have proven effective for reducing detection limits for biosensing assays, the techniques are not capable of reducing limits of detection and quantitation to the ultimate limit of digital resolution, in which each detected molecule may be counted individually 16, 17 . While digital resolution biodetection may be achieved through partitioning of the sample into thousands of individual droplets, followed by enzymatic amplification, as with ddPCR 18 , BEAMing 19 , and Quanterix Simoa™ assays 20 , we seek a more direct and simple approach in which a nanoparticle tag is attached to each target molecule, and a simple and inexpensive optical detection instrument counts the tags with high signal-to-noise ratio.…”