An antibody-free microfluidic paper-based analytical device for the determination of tear fluid lactoferrin by fluorescence sensitization of Tb³⁺

An inkjet-printed microfluidic paper-based analytical device (μPAD) for the detection of lactoferrin has been developed. The analyte concentration dependent fluorescence emission, caused by the sensitization of pre-deposited terbium (Tb³⁺) upon complexation with lactoferrin on the paper device, is captured using a digital camera. The dynamic response range (0.5-3 mg mL⁻¹) and the limit of detection (0.30 mg mL⁻¹) of the μPAD are suitable for the analysis of normal human tears and the detection of eye disorders. Finally, lactoferrin concentrations in human tear samples were analyzed by the μPADs and the assay results corresponded within 6% error to those obtained by an immunoassay (ELISA). The μPADs provide a simple, rapid and accurate method for lactoferrin detection in tear fluid. Results are obtained within 15 min of a single application of 2.5 μL of sample. To the best of our knowledge, this is the first report of a device for lactoferrin quantification relying neither on an immunoassay nor on high cost analytical instrumentation.