Simple and sensitive turn-on luminescent detection of biothiols based on energy transfer between green-emitting upconversion nanocrystals and gold nanoparticles

We have constructed a nanoconjugate composed of positively charged NaYF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs) and negatively charged gold nanoparticles (AuNPs). Fluorescence resonance energy transfer occurs between the UCNPs and the AuNPs. If the AuNPs interact with thiols, this will cause aggregation and lead to the decreased absorption by the AuNPs. As a result, the luminescence intensity of the UCNPs will be restored. This finding was explored to design a simple and sensitive luminescence assay for biothiols including cysteine, homocysteine. Under the optimal conditions, the calibration plot is linear in the range from 0.04 to 1.00 mu g mL(-1) of cysteine, and from 0.06 to 1.80 mu g mL(-1) of homocysteine. This method was applied to the determination of cysteine in synthetic samples.