One-pot fabrication of highly stable and luminescent InP quantum dots nanobeads through multifunctional polymer...

Lateral flow immunoassay (LFIA) with the advantages of simplicity, rapidness, and low cost have been a prominent point-of-care test (POCT) technology in invitro diagnostics (IVD). Quantum dots (QDs) based-LFIA have attracted strong attention due to higher sensitivity and quantitative capabilities. Developing the less toxic InP QDs, the most promising candidate for Cd-based QDs, can advance their practical applications in industrial products. However, the use of InP QDs as fluorescence label in LFIA is limited by their unstable and poor luminescent properties due to their highly susceptibility towards O₂ and H₂O.

We developed a one-pot approach to fabricate InP nanobeads (InP QBs) by emulsion evaporation and multifunctional polymer encapsulation. After the InP@DTAB nanobeads formed by emulsion-solvent evaporation with dodecyl trimethylammonium bromide (DTAB), the InP@DTAB nanobeads were encapsulated with PVP and carboxyl PEG. This method not only minimizes fluorescence loss caused by defects in multi-step reactions but also directly introduces carboxyl groups, facilitating subsequent conjugation with biomolecules. The prepared InP QBs showed high brightness, good alkaline resistance, photostability and thermal stability. Subsequently, the InP QBs was used as labels in LFIA for detection of C-reactive protein (CRP) and N-terminal pro-B-type natriuretic peptide (NT-proBNP), achieving lower detection limits of 0.67 ng/mL for CRP and 0.003 ng/mL for NT-proBNP. The InP QBs based-LFIA also had excellent specificity, stability, and accuracy verified by clinical samples.

This study illustrates the first introduction of PVP and carboxyl PEG to prepare InP nanobeads after the nanobeads formed with emulsion evaporation, which avoided the method of silica encapsulation leading to the fluorescence quench. The InP nanobeads retains the fluorescence and their stability was greatly improved. Compared to other point-of-care test (POCT) assay, the developed InP QBs based-LFIA achieves lower detection limits with excellent specificity, stability, especially accuracy, which shows great application prospects for POCT kits.