Fluorescent polarity probes for identifying bovine serum albumin: Amplification effect of para-substituted benzene

• Three coumarin-based fluorescent probes for polarity were synthesized.
• Compound 3 exhibited significantly solvatochromic UV–vis and fluorescence spectra.
• The addition of BSA induced evident fluorescence enhancement with ∼60 nm blue shift in the emission band of probe 3.
• Probe 3 could measure BSA content in fetal bovine serum with good recovery.

Fluorescent probes 1–3 with coumarin as the fluorophore were designed and synthesized for the determination of bovine serum albumin (BSA). All three probes exhibited evidently solvatochromic UV–vis and fluorescence spectra. Compound 3 was the most effective towards the solvent's polarity: 155 nm (vs. 60 nm for 1 and 100 nm for 2) red shift in the emission maximum was found as the solvent changing from cyclohexane to phosphate buffer solution. These compounds were applied to detect BSA based on the hypothesis that the polarity of the microenvironment surrounding the probe will undergo significant change when the probe moves from the bulk solution to the hydrophobic domains of BSA. 3 was the most sensitive towards BSA and the detection limit of BSA was 0.6 μg/mL with 3 as the probe, which ensured the detection of BSA content in fetal bovine serum with good recovery.