Near-Infrared Metal-Enhanced Fluorescence Using a Liquid–Liquid Droplet Micromixer in a Disposable Poly(Methyl Methacrylate) Microchip

Abstract

Solution-based metal-enhanced fluorescence of near-infrared fluorophores in a poly(methyl methacrylate) microchip is studied. A liquid-liquid droplet micromixer is used for rapid mixing of fluorophores with silver nanoparticles while maintaining discrete packets of known analytes for reproducible quantitative analysis. Nanoparticle aggregation within the microchip is controlled by individually adjusting salt concentration, colloid concentration, and mixing efficiency. Results identify an optimal salt concentration for aggregate formation and enhanced fluorescence, while the impacts of colloid concentration and mixing efficiency increase linearly, suggesting the possibility of further enhancement. Fluorescence enhancements of 35-fold were achieved on a microfluidics device using metal-enhanced fluorescence in a discrete solution-based system with exposure times of only 50 ms.

Exploiting the light–metal interaction for biomolecular sensing and imaging

“…By making use of the plasmonic enhancement of nanorods and nanoshells, Halas and co-workers have demonstrated that NIR dyes can be as efficient as organic dye molecules in the visible range (Bardhan et al 2009; Tam et al 2007). Recently, metal enhanced fluorescence has been applied in microfluidic chips to enhance the detection efficiency of NIR dye labels (Furtaw et al 2009). Metal nanoparticles have also been employed in therapeutic applications, such as photothermal cancer therapy.…”

A Near-Infrared, Surface-Enhanced, Fluorophore-Linked Immunosorbent Assay

“…Third, aggregation has been known to broaden and red-shift the resonant frequency of AgNPs by enabling multipole plasmon modes and thus increases the interaction with NIR light [see Figure b]. Aggregation of AgNP has also been shown to generate small, localized, enhanced electromagnetic fields, known as “hot spots”, thereby enabling significant SEF of appropriately located fluorophores. ,,, Therefore, a combination of enhanced near-field due to aggregation with low far-field losses and the maximized quality factor makes NIR-SEF with AgNPs in solution a powerful technology.…”

“…When certain criteria are met, the radiative decay dominates nonradiative processes, which along with the enhanced excitation rate can significantly increase the quantum yield. Enhanced signal intensity from SEF along with lower background via NIR fluorophores has been shown to provide substantial improvement to fluorescence sensitivity. , NIR-SEF has been demonstrated previously with gold nanostructures on surfaces, − gold nanoparticles in solution, − silver nanostructures on surfaces, ,,, and silver nanoparticles in solution. , …”

Droplet Enhanced Fluorescence for Ultrasensitive Detection Using Inkjet

“…The improved local electromagnetic field at an interface was confirmed to greatly excite neighboring atoms, molecules and nanomaterials thus enhancing fluorescence, Raleigh scatting and Raman scatting 21 . If the interface is located on a smaller surface 22 , the interfacial fluorescence would be further enhanced by the additionally surficial activation energy of quantum dots 23,24 , nanotubes 25 , nanoparticles [26][27][28] , nanoclusters 29 and 2 dimensional nanoparticle sheets 30 as well. However, our current knowledge of liquid interface enhanced fluorescence is limited because of difficulties related to observing the liquidliquid interface.…”

“…In addition, the enhanced fluorescence can be further intensified by a surficial plasma at the interface, which excites the closed fluorophores or dipoles, thus enhancing the interfacial fluorescence. − Investigations of plasmatic enhanced fluorescence have mainly focused on metal surface enhanced fluorescence. − The improved local electromagnetic field at an interface was confirmed to greatly excite neighboring atoms, molecules, and nanomaterials and thus enhance fluorescence, Raleigh scattering, and Raman scattering . If the interface is located on a smaller surface, the interfacial fluorescence would be further enhanced by the additional surficial activation energy of quantum dots, , nanotubes, nanoparticles, − nanoclusters, and 2-dimensional nanoparticle sheets as well. However, our current knowledge of liquid interface enhanced fluorescence is limited because of difficulties related to observing the liquid–liquid interface.…”