Magnetic lateral flow strip (MLFS) based on magnetic bead (MB) and smart phone camera has been developed for quantitative detection of cocaine (CC) in urine samples. CC and CC-bovine serum albumin (CC-BSA) could competitively react with MB-antibody (MB-Ab) of CC on the surface of test line of MLFS. The color of MB-Ab conjugate on the test line relates to the concentration of target in the competition immunoassay format, which can be used as a visual signal. Furthermore, the color density of the MB-Ab conjugate can be transferred into digital signal (gray value) by a smart phone, which can be used as a quantitative signal. The linear detection range for CC is 5–500 ng/mL and the relative standard deviations are under 10%. The visual limit of detection was 5 ng/mL and the whole analysis time was within 10 min. The MLFS has been successfully employed for the detection of CC in urine samples without sample pre-treatment and the result is also agreed to that of enzyme-linked immunosorbent assay (ELISA). With the popularization of smart phone cameras, the MLFS has large potential in the detection of drug residues in virtue of its stability, speediness, and low-cost.

We developed a competitive colorimetric nanosensor based on Au@Ag bimetallic nanoparticles for the detection of interleukin-6 (IL-6) in clinical samples. Antibody-conjugated magnetic nanoparticles (MNPs) and polystyrene (PS) microparticles conjugated with both catalase and a secondary antibody can form sandwich structures that enable one-step target enrichment and separation. The catalase on the surface of the PS can catalyze the hydrolysis of hydrogen peroxide (H₂O₂) to regulate the deposition of Ag⁺ on the surface of gold nanoparticles (AuNPs), and forms different sizes and amounts of Au@Ag bimetallic nanoparticles (Au@AgNPs) which produce a distinct color signal for readout with the naked eye. Our sensor features high sensitivity, selectivity, reproducibility and anti-interference property as a result of comprehensive parameter optimization. The limit of detection of IL-6 can reach 11 pg mL⁻¹ with the naked eye and 1.2 pg mL⁻¹ by quantitative instrumental analysis. The whole analysis can be finished within 1 h. More importantly, we successfully apply our platform or the detection of IL-6 in clinical samples with better accuracy than conventional enzyme-linked immunosorbent assay (ELISA).