Solvent optimization and fluorescein lasing for avidin biosensing

• Narrow fluorescein emission is a viable tool for protein biosensing. • Solvent optimization enabled narrow fluorescein emission. • 1:1 methanol-NSS mixture achieves optimal optical performance. • Optimal solvent and energy allow 4.38 nm bandwidth in the Littrow-like cavity. • Spectra changes were observed as a function of the amount of avidin in the solution. We report pulsed laser emission using fluorescein combined with avidin as an active medium matrix in a Littrow-like configuration system. The study covers testing several solvents and a range of excitation energies, aiming to get the narrowest bandwidth for stable peak emission wavelength. Initially, for 4 mM of fluorescein in 1:1 mixture of methanol-NSS, and excited with 20.80mJ of energy, a laser mission of 4.38 nm bandwidth is achieved. Then, different concentrations of thiolated avidin are mixed in the active medium, causing related red-shifts over the initial emission band. Substantial spectral changes are observed down to 0.3 μM of avidin, making apparent the stability conditions for this sort of laser system to work out as a biosensor.