A Continuous-Flow System for High-Precision Kinetics Using Small Volumes

Modern advancements in continuous-flow aided kinetic analysis

Although kinetic analysis has traditionally been conducted in a batch vessel, continuous-flow aided kinetic analysis continues to swell in popularity.

Continuous-flow injection microfluidic thrombin assays: The effect of binding kinetics on observed enzyme inhibition

A microfluidic assay for monitoring the inhibition of thrombin peptidase activity was developed. The system, which utilised soluble reagents in continuous-flow injection mode, was configured so as to allow inhibitor titrations via gradient formation. This microfluidic continuous-flow injection titration assay (CFITA) enabled the potency of a set of small-molecule serine peptidase inhibitors (SPIs) to be evaluated. The results, compared to standard microtiter plate (MTP) data, indicated that a microfluidic CFITA provided an efficient and effective method for evaluating compound potency. Crucially, whereas for fast-acting compounds the rank order of potency between the CFITA and MTP methods was preserved, for slow-acting compounds the observed CFITA potencies were significantly lower. These results, in conjunction with data from computer simulations, clearly demonstrated that continuous-flow assays, and perhaps microfluidic assays in general, must take into account binding kinetics when used to assess reaction criteria.

Flow-based systems for rapid and high-precision enzyme kinetics studies

Enzyme kinetics studies normally focus on the initial rate of enzymatic reaction. However, the manual operation of steps of the conventional enzyme kinetics method has some drawbacks. Errors can result from the imprecise time control and time necessary for manual changing the reaction cuvettes into and out of the detector. By using the automatic flow-based analytical systems, enzyme kinetics studies can be carried out at real-time initial rate avoiding the potential errors inherent in manual operation. Flow-based systems have been developed to provide rapid, low-volume, and high-precision analyses that effectively replace the many tedious and high volume requirements of conventional wet chemistry analyses. This article presents various arrangements of flow-based techniques and their potential use in future enzyme kinetics applications.

Improved method for kinetic studies in microreactors using flow manipulation and noninvasive Raman spectrometry

A novel method has been devised to derive kinetic information about reactions in microfluidic systems. Advantages have been demonstrated over conventional procedures for a Knoevenagel condensation reaction in terms of the time required to obtain the data (fivefold reduction) and the efficient use of reagents (tenfold reduction). The procedure is based on a step change from a low (e.g., 0.6 μL min(-1)) to a high (e.g., 14 μL min(-1)) flow rate and real-time noninvasive Raman measurements at the end of the flow line, which allows location-specific information to be obtained without the need to move the measurement probe along the microreactor channel. To validate the method, values of the effective reaction order n were obtained employing two different experimental methodologies. Using these values of n, rate constants k were calculated and compared. The values of k derived from the proposed method at 10 and 40 °C were 0.0356 ± 0.0008 mol(-0.3) dm(0.9) s(-1) (n = 1.3) and 0.24 ± 0.018 mol(-0.1) dm(0.3) s(-1) (n = 1.1), respectively, whereas the values obtained using a more laborious conventional methodology were 0.0335 ± 0.0032 mol(-0.4) dm(1.2) s(-1) (n = 1.4) at 10 °C and 0.244 ± 0.032 mol(-0.3) dm(0.9) s(-1) (n = 1.3) at 40 °C. The new approach is not limited to analysis by Raman spectrometry and can be used with different techniques that can be incorporated into the end of the flow path to provide rapid measurements.

Expansion channels for low-pass filtering of axial concentration gradients in microfluidic systems

Chemical gradients that run axially in a microfluidic channel often contain undesirable high-frequency concentration variations, or noise, that results from mechanical and thermal fluctuations in the system. In this paper, we describe a passive microfluidic component called an 'expansion channel' (EC), that removes high frequency noise through axial dispersion. We show that the behavior of the filter can be modeled analytically, using an expression for the transfer function of the microfluidic channel, derived by Xie et al. (Y. W. Xie, L. Chen and C. H. Mastrangelo, Lab Chip, 2008, 8, 907-912). The use of ECs to remove noise from gradients formed in enyzmatic assays in a microfluidic channel is demonstrated. The resulting data quality is improved which enables better fits to chemical models and more accurate analysis. ECs should be very effective in removing noise from axial concentration gradients found in many microfluidic applications, e.g. liquid chromatography, biochemistry, and chemotaxis studies.