Effect of gold nanoparticles on thermal gradient generation and thermotaxis of E. coli cells in microfluidic device

Abstract

Bacteria responds to changing chemical and thermal environment by moving towards or away from a particular location. In this report, we looked into thermal gradient generation and response of E. coli DH5α cells to thermal gradient in the presence and in the absence of spherical gold nanoparticles (size: 15 to 22 nm) in a static microfluidic environment using a polydimethylsiloxane (PDMS) made microfluidic device. A PDMS-agarose based microfluidic device for generating thermal gradient has been developed and the thermal gradient generation in the device has been validated with the numerical simulation. Our studies revealed that the presence of gold nanoparticles, AuNPs (0.649 μg/mL) has no effect on the thermal gradient generation. The E. coli DH5α cells have been treated with AuNPs of two different concentrations (0.649 μg/mL and 0.008 μg/mL). The thermotaxis behavior of cells in the presence of AuNPs has been studied and compared to the thermotaxis of E.coli DH5α cells in the absence of AuNPs. In case of thermotaxis, in the absence of the AuNPs, the E. coli DH5α cells showed better thermotaxis towards lower temperature range, whereas in the presence of AuNPs (0.649 μg/mL and 0.008 μg/mL) thermotaxis of the E. coli DH5α cells has been inhibited. The results show that the spherical AuNPs intervenes in the themotaxis of E. coli DH5α cells and inhibits the cell migration. The reason for the failure in thermotaxis response mechanism may be due to decreased F-type ATP synthase activity and collapse of membrane potential by AuNPs, which, in turn, leads to decreased ATP levels. This has been hypothesized since both thermotaxis and chemotaxis follows the same response mechanism for migration in which ATP plays critical role.

Interplay of chemical and thermal gradient on bacterial migration in a diffusive microfluidic device

“…1). 15 Computations have been performed to gauge the characteristics of the generated gradient since the chemicals used in the experiments are colorless, and hence, the gradient cannot be determined quantitatively during experiments. The chemical and thermal gradient generation within the device has been already characterized and validated with the "solute transport" and "conjugate heat transfer" modules of COMSOL Multiphysics, 4.2.a., in previous reports by the same authors.…”

“…The chemical and thermal gradient generation within the device has been already characterized and validated with the "solute transport" and "conjugate heat transfer" modules of COMSOL Multiphysics, 4.2.a., in previous reports by the same authors. 11,15 Accordingly, the same simulation protocol has been used in the present study to estimate a priori steady combined chemical (sorbitol/NiSO 4 ) and thermal gradient generation in the designed device. The boundary conditions are similar to those reported by the present authors.…”

“…The boundary conditions are similar to those reported by the present authors. 11,15 A PDMS (polydimethysiloxane) based device was fabricated using optical and soft lithography techniques. 15…”

“…As chemical and thermal gradients are among the most important agents affecting the migration pattern of microbial cells within a physiological system, the effects of these individual gradients on E. coli have been reported by researchers. 5,[8][9][10][11][12][13][14][15] Earlier, conventional methods such as capillary assay 8 and Boyden chamber 9 have been used to generate chemical gradients to study the chemotaxis of E. coli cells in vitro. Agar plates placed over aluminum blocks with provision for the flow of hot and cold fluids 10 were used to generate thermal gradients to study the thermotaxis of E. coli cells.…”

“…5 This is due to the fact that microfluidic environments can successfully mimic the requisite physiological conditions, both qualitatively and quantitatively. There have been reports on individual studies of E. coli cell migration due to chemical 5,[11][12][13] and thermal gradients 14,15 using microfluidic devices.…”