The Bathtub Method for Detecting Small Quantities of Specific Pathogens

Abstract

Current techniques used to concentrate pathogens, such as centrifugation and size-exclusion filtration, are non-specific for pathogens of interest and inefficient to deal with large volumes of liquids and liquid foods. In addition, the isolated pathogens need to be analyzed subsequently with expensive, laborious, sample-based lab methods (e.g., culturing and PCR) that do not enable rapid identification of the pathogens. This paper presents a revolutionary method for the capture and rapid detection of small amounts of specific bacteria from entire liquid streams. The method combines a volumetric biomolecular filter and an automated biosensor measurement system. The volumetric biomolecular filter is a three-dimensional, multi-layered net with each layer made up of hundreds of phage-coated magnetoelastic (ME) biosensors with a pre-determined resonant frequency. These biosensors are arrayed with a desired spacing and held flexibly (i.e., cantilever-like configuration) on an electro-magnetized silicon steel comb structure. The phage that is coated on the biosensors are responsible for capturing a specific pathogen. In this way, only the pathogen of interest can be captured on the filter whereas the other matters (non-specific pathogens, debris, etc.) are allowed to pass. In addition, the biosensors can bend over for large, heavy debris, eliminating a common issue of clogging found in the current filtration techniques. Once the entire liquid is flowed over, the biosensors on the filter are transferred into etched cavities on a silicon wafer by shutting off the electromagnetic field. These etched cavities are indexed such that a surface-scanning detector can be used to wirelessly measure the biosensors sequentially in an automated manner. The resonant frequency changes of the biosensors due to the attachment of the pathogen can be measured in 250 milliseconds per sensor. The presented method enables the evaluation of large volumes of liquids for the presence of small numbers of pathogens. The capture efficiency of pathogens was found to be dependent on the filter design.