Novel instrumentation and biomedical applications of very near-infrared fluorescence

A high wavelength fluorescent probe, Nile Red, was added to four proteins, viz., bovine albumin, alpha1-acid glycoprotein, beta-lactoglobulin and ovomucoid. Nile Red showed an enhancement in fluorescence and a shift in emission wavelength, suggesting it was bonding hydrophobically to these proteins. Drug displacement of Nile Red from alpha1-acid glycoprotein was achieved with both D,L-propranolol and flufenamic acid, showing that the binding site is less electrostatic and more hydrophobic in nature. In order to monitor these interactions, a simple spectrofluorimeter was constructed from solid-state components; the sensitivity of this instrument compared well with that of standard laboratory spectrofluorimeters.