Combining droplet microfluidics and magnetoresistive sensors for the rapid and quantitative detection of Klebsiella pneumoniae in urinary tract infections

Urinary tract infections (UTIs) are one of the most common bacterial infections and are considered a public health problem. This has been exacerbated due to the increasing prevalence of multidrug-resistant bacterial strains which poses a significant concern. Additionally, current diagnostic methods are time-consuming and laborious, hindering appropriate treatment and infection control. Herein a novel microfluidic system for diagnosis of UTIs caused by Klebsiella pneumoniae is presented, relying on the unprecedented combination of magnetoresistive (MR) sensors with droplet microfluidics. Initially, K. pneumoniae suspensions were encapsulated in droplets with magnetic nanoparticles (MNPs) functionalized with a bacteriophage receptor binding protein (RBP) specific for K. pneumoniae. The magnetically labeled cells inside droplets were further detected through an MR readout system. This strategy enabled the refined control over the number of MNPs and bacteria inside each droplet which allowed the clear discrimination between the output signals from samples of K. pneumoniae and non-target Escherichia coli. In addition, a direct correlation of the number of events from the MR sensors with different concentrations of K. pneumoniae was observed, providing a dynamic detection range of this pathogen from 104 to 108 CFU/mL. The developed device was further validated for the detection of K. pneumoniae in urine clinical samples (UCSs) from patients with UTIs. These samples were directly encapsulated with RBPfunctionalized MNPs, with no need for sample pre-treatment. This allowed the quantitative detection of K. pneumoniae in UTIs samples with high specificity (100%) and sensitivity (87.5%) in less than 1 h.