Direct detection of whole bacteria using a nonlinear acoustic resonator

Shilpa Khobragade,Carlos Da Silva Granja,Niklas Sandström,Igor Efimov,Victor P Ostanin,Wouter Van Der Wijngaart,David Klenerman,Sourav K Ghosh

doi:10.1016/j.snb.2020.128086

Abstract

Direct detection of whole vegetative bacteria was investigated employing a quartz crystal resonator (QCR) in its nonlinear regime. Escherichia coli (E. coli) in buffer solution under flow was captured on a QCR in a microfluidic cell using a whole-cell anti-E.coli aptamer. The nonlinear distortion in QCR response due to the ‘pull’ from surface-bound bacteria was measured in realtime as the change in third Fourier harmonic (3f) current and compared with shifts in the traditional acoustic parameters of resonance frequency and dissipation. The change in 3f current showed superior quantitative correlation with E. coli concentrations (105-108 cfu/mL) and at least an order of magnitude better sensitivity than shifts in the traditional acoustic parameters. Most interestingly, underpinned by the strength of bacteria-QCR pull, the nonlinear acoustic principle demonstrated a unique specificity in transduction, even in a mixed sample with another gram-negative bacteria, that can supplement the specificity of the bioreceptors. An analytical expression was derived to quantitatively relate the competing influence of shifts in dissipation and nonlinearity coefficient of the QCR on the change in 3f current. This study demonstrates the potential for reliable direct readout of bioreceptor-mediated binding of whole vegetative bacteria from complex samples using a nonlinear acoustic resonator.

Highlights

Despite advancements in the knowledge of infectious disease, improved sanitation, effective vaccines and antimicrobial drugs, infectious diseases continue to be a global public health problem [1]
This study investigated for the first time the change in nonlinear acoustic response of a quartz crystal resonator (QCR) due to aptamer-mediated binding of whole vegetative bacteria, and the feasibility of using this change for their reliable direct detection from pure and mixed samples in buffer
As the 3f current is directly related to the 1f current as in Eq 4, the graph of 3f current bears a similarity with the QCR’s fundamental resonance characteristics but with some influence from the third overtone resonance characteristics when the 3f frequency is near the third overtone resonance frequency

Summary

Introduction

Despite advancements in the knowledge of infectious disease, improved sanitation, effective vaccines and antimicrobial drugs, infectious diseases continue to be a global public health problem [1]. Definitive diagnosis, involving identification of the bug and an appropriate antimicrobial drug, enables early initiation of optimised treatment. Current diagnostic techniques, namely microscopy, cell culture, biochemical and immunological assays, and genetic analysis, are largely laboratory-based, time-consuming, skill-demanding, and unavailable at the point of care [2]. The delay and, in some cases, absence of appropriate treatment have continued to contribute to high mortality and morbidity, prolonged recovery time and rising economic costs [3]. The widespread prescription of unnecessary or inappropriate antimicrobials has given rise to antimicrobial resistance, which has assumed the scale of a global threat. There is an urgent need for portable, affordable and easy-to-use tests that can rapidly identify the causal pathogens and appropriate antimicrobials at the point-of-care [4].

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Discussion

Conclusion