Surface plasmon-coupled directional fluorescence emission

Attomolar analyte sensing techniques (AttoSens): a review on a decade of progress on chemical and biosensing nanoplatforms

Detecting the ultra-low abundance of analytes in real-life samples, such as biological fluids, water, soil, and food, requires the design and development of high-performance biosensing modalities. The breakthrough efforts from the scientific community have led to the realization of sensing technologies that measure the analyte's ultra-trace level, with relevant sensitivity, selectivity, response time, and sampling efficiency, referred to as Attomolar Analyte Sensing Techniques (AttoSens) in this review. In an AttoSens platform, 1 aM detection corresponds to the quantification of 60 target analyte molecules in 100 μL of sample volume. Herein, we review the approaches listed for various sensor probe design, and their sensing strategies that paved the way for the detection of attomolar (aM: 10^-18 M) concentration of analytes. A summary of the technological advances made by the diverse AttoSens trends from the past decade is presented.

Multi-wavelength immunoassays using surface plasmon-coupled emission

We describe a new method for multi-wavelength immunoassays using surface plasmon-coupled emission (SPCE). This phenomenon is coupling of excited fluorophores with a nearby thin metal film, in our case silver, resulting in strongly directional emission into the underlying glass substrate. The angle at which the radiation propagate through the prism depends on the surface plasmon angle for the relevant wavelength. These angles depend on emission wavelength, allowing measurement of multiple analytes using multiple emission wavelengths. We demonstrated this possibility using antibodies labeled with either Rhodamine Red-X or AlexaFluor 647. These antibodies were directed against an antigen protein bound to the silver surface. The emission from each labeled antibody occurred at a different angle on the glass prism, allowing independent measurement of surface binding of each antibody. This method of SPCE immunoassays can be readily extended to 4 or more wavelengths.