Microfluidic paper-based analytical aptasensor for fluorometric -lactoglobulin determination

Herein, we present a new luminescent -based analytical method for sensitive fluorometric determination of a milk allergen, beta-lactoglobulin (beta-LG), in food products based on a portable, low-cost, and easy -to -use microfluidic paper -based analytical device (mu PAD). For this purpose, the developed mu PAD consisted on a beta-LG specific aptamer immobilized on a cellulose disk, and fluorescent Carbon Quantum Dots (CQDs) bioconjugated with its complementary oligonucleotide (DNA), which worked as a label for the aptamer hybridization and its complementary DNA (CQDs-DNA). In a sample with beta-LG, the aptamer preferentially binds to beta-LG protein and this leads to release of the CQDs-DNA. After washing the mu PAD, where the aptamer is immobilized, detection is achieved by fluorescence intensity decrease. An estimation of beta-LG concentration can be calculated thanks to the fluorescence changes, for that, a photo of the mu PAD is taken using either a digital camera or a smartphone. The mu PAD showed an excellent detection response for beta-LG in the range of 1.8 to 500 ng/mL with a limit of detection of up to 0.6 ng/mL using the digital camera. Furthermore, the developed method was successfully applied to the determination of beta-LG in food samples such as skimmed milk, crispy rice, cookies and chocolate.