Development of a photothermal bead-based nucleic acid amplification test (pbbNAAT) technique for a high-performance loop-mediated isothermal amplification (LAMP)–based point-of-care test (POCT)

We have developed a novel molecular diagnostic platform (photothermal bead-based nucleic acid amplification test; pbbNAAT) that greatly improves the low sensitivity of direct loop-mediated isothermal amplification (LAMP) and allows for specific detection of LAMP amplicons in complex samples. The pbbNAAT integrates specific ligand-functionalized polypyrrole-coated iron oxide particles (PPy@IOs) capable of photothermal conversion and single-molecule magnetic capture of target analytes, the released nucleic acid, and LAMP-amplified products under external light energy control and magnetic manipulations. This allows for sample pretreatment, pbbLAMP amplification, and subsequent amplicon detection with bead-based ELISA in a one-stop microreactor without loss. In addition, photonic heating with PPy@IOs and external light control provide instant and uniform heating for thermolysis and pbbLAMP implementations. Moreover, it generates higher primer annealing stringency for LAMP primers in pbbLAMP; thus, it can detect pathogen-specific DNA accurately and promptly in pathogen-spiked complex materials. The sample pretreatment procedure of pbbNAAT can greatly reduce inhibitors originating from complex samples, which enables the maintenance of maximal enzyme activities for highly sensitive detection. More importantly, the pbbLAMP assay coupled with magnetic capture permits subsequent bead-based ELISA detection to determine true positive LAMP amplicons on PPy@IOs. The pbbNAAT platform has a high tolerance to inhibitors originating from complex samples, high analytical specificity, and limitation of detection (LoD) as low as 8 CFU/reaction to detect E. coli spiked in human whole blood, bovine milk, and can be completed in less than 1 h. Therefore, we believe that pbbNAAT can serve as a suitable direct LAMP platform for on-site POCTs.