skip to main content


Title: 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.  more » « less
Award ID(s):
1900277
NSF-PAR ID:
10428315
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Nature Communications
Volume:
13
Issue:
1
ISSN:
2041-1723
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Unlike normal fluorescent methods that use the intensity as a direct measurement of the localized enhanced field, we use blinking statistics of quantum dots (QDs). We have already shown that blinking gives a more accurate characterization of the near-field. When an emitter is situated close to a metallic surface, non-radiative pathways are opened up, leading to quenching of the exciton. Blinking statistics, however, is only minimally affected by quenching, and therefore can be used to probe emitters in close proximity to metallic surfaces. We have expanded our method (COFIBINS) to high densities using superresolution technique SOFI. A proof of principle for SOFI-COFIBINS is demonstrated with a defocused point spread function. The method is then applied to surface plasmon polaritons. SOFI-COFIBINS shows excellent agreement with the average fluorescence intensity. 
    more » « less
  2. Plasmonic and photonic technologies have attracted strong interest in the past few decades toward several interdisciplinary applications stemming from unique light-matter interactions fostered by materials at the nanoscale. The versatility of plasmonic and photonic sensors for ultrasensitive, rapid, analyte sensing without extensive sample pre-treatment steps or sophisticated optics have resulted in their strong foothold in the broad arena of biosensing. Fluorescence-based bioanalytical techniques are widely used in liquid-biopsy diagnostics applications, but require many labeled target molecules to combine their emission output to achieve a practically useful signal-to-noise ratio. Approaches capable of amplifying fluorescence signals can provide signal-to-noise sufficient for digitally counting single emitters for ultrasensitive assays that are detected with simple and inexpensive instruments. [1]. Plasmonic and nano-photonics can function in synergy to amplify fluorescence signals. By concentrating optical energy well below the diffraction limit, plasmonic nanoantenna provide spatial control over excitation light, but their quality factor (Q) is modulated by radiative and dissipative losses. Photonic crystals (PC) as dielectric microcavities have a diffraction-limited optical mode volume despite being able to generate a high Q-factor. Here, we demonstrate a plasmonic-photonic hybrid system to produce a much stronger fluorescent enhancement for digital resolution biosensing. With an optimized dielectric spacer layer, around 200 Alexa-647 fluorophores have been coated over heterometallic Ag@Au core-shell plasmonic nanostructures with minimized Ohmic losses and quenching effects [2]. The target-specific molecule capture events enabled this plasmonic fluor to attach to the PC surface, forming a Plasmonic-Photonic hybrid mode. With much stronger local field enhancement, far-field directional emission, large Purcell enhancement, and high quantum efficiency, we report a two-orders signal enhancement from PC-enhanced plasmonic-fluor (104-fold brighter than a single fluorophore). This improved signal-to-noise ratio enabled us to perform single molecule imaging even with a 10x (NA=0.2) objective lens while offering 3 orders of magnitude boost in the limit of detection of Interleukine-6 (common biomarker for cancer, inflammation, sepsis, and autoimmune disease) compared with standard immunoassays in human plasma 
    more » « less
  3. Abstract

    We present a novel ligand, 5‐norbornene‐2‐nonanoic acid, which can be directly added during established quantum dot (QD) syntheses in organic solvents to generate “clickable” QDs at a few hundred nmol scale. This ligand has a carboxyl group at one terminus to bind to the surface of QDs and a norbornene group at the opposite end that enables straightforward phase transfer of QDs into aqueous solutions via efficient norbornene/tetrazine click chemistry. Our ligand system removes the traditional ligand‐exchange step and can produce water‐soluble QDs with a high quantum yield and a small hydrodynamic diameter of approximately 12 nm at an order of magnitude higher scale than previous methods. We demonstrate the effectiveness of our approach by incubating azido‐functionalized CdSe/CdS QDs with 4T1 cancer cells that are metabolically labeled with a dibenzocyclooctyne‐bearing unnatural sugar. The QDs exhibit high targeting efficiency and minimal nonspecific binding.

     
    more » « less
  4. Abstract

    We present a novel ligand, 5‐norbornene‐2‐nonanoic acid, which can be directly added during established quantum dot (QD) syntheses in organic solvents to generate “clickable” QDs at a few hundred nmol scale. This ligand has a carboxyl group at one terminus to bind to the surface of QDs and a norbornene group at the opposite end that enables straightforward phase transfer of QDs into aqueous solutions via efficient norbornene/tetrazine click chemistry. Our ligand system removes the traditional ligand‐exchange step and can produce water‐soluble QDs with a high quantum yield and a small hydrodynamic diameter of approximately 12 nm at an order of magnitude higher scale than previous methods. We demonstrate the effectiveness of our approach by incubating azido‐functionalized CdSe/CdS QDs with 4T1 cancer cells that are metabolically labeled with a dibenzocyclooctyne‐bearing unnatural sugar. The QDs exhibit high targeting efficiency and minimal nonspecific binding.

     
    more » « less
  5. Photon upconversion in systems incorporating inorganic quantum dots (QDs) is of great interest for applications in solar energy conversion, bioimaging, and photodynamic therapy. Achieving high up-conversion efficiency requires not only high-quality inorganic nanoparticles, but also precise control of their surface functional groups. Gas-phase surface functionalization provides a new pathway towards controlling the surface of small inorganic nanoparticles. In this contribution, we utilize a one-step low-temperature plasma technique for the synthesis and in-flight partial functionalization of silicon QDs with alkyl chains. The partially functionalized surface is then modified further with 9-vinylanthracene via thermal hydrosilylation resulting in the grafting of 9-ethylanthracene (9EA) groups. We have found that the minimum alkyl ligand density necessary for quantum dot solubility also gives the maximum upconversion quantum yield, reaching 17% for silicon QDs with Si-dodecyl chains and an average of 3 9EA molecules per particle. 
    more » « less