Elution of Artificial Sputum from Swab by Rotating Magnetic Field-Induced Mechanical Impingement

Abstract

Cotton-tipped applicator swabs are used as a collection device for many biological samples and its complete elution is a desired step for clinical and forensic diagnostics. Swabs are used to collect infectious body fluids, where the concentration of pathogens can range from 1 × 10 4 CFU/mL (colony forming units/mL) in respiratory-tract infections and 1 × 10 5 in urinary-tract infections, to up to 1 × 10 9 CFU/mL in salivary samples. These samples are then eluted and lysed, prior to DNA (De-oxy Ribonucleic Acid) analysis. The recovery of micro-organisms from a matrix of swab fibres depends on the nature of the body fluid, the type of the swab fibres, and the process of elution. Various methods to elute samples from swab include chemical digestion of fibres (~20% recovery), centrifugation (~58% recovery), piezoelectric vibration, or pressurized fluid-flow (~60% recovery). This study reports a magnetically-actuated physical impingement method for elution and recovery of artificial sputum samples from cotton fibres. A device has been fabricated to induce a rotating magnetic field on smaller magnetic particles in a vial that strikes the swab within a confined gap. Elution from the swab in this device was characterized using 2% Methyl cellulose in deionised water, loaded with fluorescent-tagged polystyrene beads and E. coli at various concentrations. The recovery efficiency was found to increase with both rotational speed and elution time, but plateaus after 400 RPM (Revolutions per minute) and 120 s, respectively. At a higher concentration of polystyrene beads (5 × 10 8 particles/mL), a maximum recovery of~85% was achieved. With lower concentration, (1 × 10 5 particles/mL) the maximum efficiency (~92.8%) was found to be almost twice of passive elution (46.7%). In the case of E. coli, the corresponding recovery efficiency at 3.35 × 10 5 CFU/mL is 90.4% at 500 RPM and 120 s. This elution method is expected to have a wide applicability in clinical diagnostics.

Diagnostics of Tuberculosis with Single-Walled Carbon Nanotube-Based Field-Effect Transistors

“…Our Ab85B-SWCNT FET devices were further studied to assess the detection of Ag85B proteins spiked in artificial sputum. The artificial sputum was prepared with 1 wt % methyl cellulose Figure a shows the I – V g curves of the Ab85B-SWCNT FET device after exposure to Ag85B solutions in artificial sputum.…”

“…The artificial sputum was prepared with 1 wt % methyl cellulose. 55 Figure 4 a shows the I – V g curves of the Ab85B-SWCNT FET device after exposure to Ag85B solutions in artificial sputum. Similar to the detection of Ag85B in PBS, a shift of the curves toward more positive gate voltage was observed, suggesting the successful detection of Ag85B proteins in artificial sputum.…”