A Portable Fluorometer with Multiple Excitation LEDs

Abstract

Fluorescent probes are widely used in biological research due to their sensitivity, selectivity, and versatility [1, 2]. Many fluorescence probes, such as fluorophores, typically have a variety of absorption and emission peaks ranging from UV to near-infrared. Therefore, a wide range of excitation wavelengths is required to simultaneously detect multiple fluorescent target analytes. Here, we propose a portable fluorometer with 13 different excitation LEDs (280 – 730 nm) that can be a viable option for simultaneously detecting multiple fluorophores. For fluorescence detection, a monochromator module was implemented to separates the color components of fluorescent emission and sequentially scan a range of wavelength (400 nm – 780 nm) with 1 nm resolution. For demonstration, fluorescein was selected as target analyte for this study. Fluorescein is an organic compound dye that is commonly used in many bioscience applications.For the excitation light source, different LEDs were used to offer a broad range of excitation wavelengths, ranging from 280 nm to 725 nm. Each LED was coupled with a color filter and a collimator lens to carry out a narrow excitation spectrum. LEDs were controlled by an LED driver IC and a microcontroller to provide a linear output current in the range of 0 to 300 mA. A multiplexer IC was implemented to sequentially turn on and off each excitation LED. The maximum absorbance and emission wavelength of fluorescein were 485 nm and 514 nm, respectively. For excitation, 434 nm LED was chosen instead of 470 nm to minimize spectral overlap between the excitation and emission spectra. The fluorescein was dissolved in methanol at a concentration of 220 mg/ml at room temperature (25 ºC). The figure shows the spectra of the excitation LED and fluorescein fluorescence measured with a developed portable fluorometer. The spectral profile of the excitation LED and the peak fluorescence of fluorescein was well-matched with previously measured value from the laboratory-based benchtop fluorometer (Fluorolog 3 FL3-22, Horiba, Japan).In summary, we have developed a portable fluorometer multiple LEDs covering a broad range of excitation wavelengths to simultaneously detect multiple fluorescent targets. Our compact fluorometer provides a viable option for multi-analyte detection in a variety of remote sensing applications such as point-of-care or environmental monitoring. Figure 1