Publication: Enhanced annihilation electrochemiluminescence by nanofluidic confinement

H. Al-Kutubi, S. Voci, L. Rassaei, N. Sojic and K. Mathwig, Chemical Science 9 (2018) 8946. [link, pdf]

toc_eclMicrofabricated nanofluidic electrochemical devices offer a highly controlled nanochannel geometry; they confine the volume of chemical reactions to the nanoscale and enable greatly amplified electrochemical detection. Here, the generation of stable light emission by electrochemiluminescence (ECL) in transparent nanofluidic devices is demonstrated for the first time by exploiting nanogap amplification. Through continuous oxidation and reduction of [Ru(bpy)3]2+ luminophores at electrodes positioned at opposite walls of a 100-nm nanochannel, we compare classic redox cycling and ECL annihilation. Enhanced ECL light emission of attomole luminophore quantities is evidenced under ambient conditions due to the spatial confinement in a 10-femtoliter volume, resulting in a short diffusion timescale and highly efficient ECL reaction pathways at the nanoscale.

Electrochemistry Symposium in Groningen

The Annual Symposium of the Working Group on Electrochemistry of the Royal Netherland Chemical Society will take place in Groningen this November:

Hyphenated Electrochemistry – Combining Electrochemical Methods with Complementary Techniques for Sensing Applications

The capability of electrochemistry is greatly enhanced when used in combination with other methods. The meeting focusses on such hyphenated techniques, which have recently gained more importance in a variety of fields, for example in analytics. Topics include single-molecule detection, electrochemiluminescence, electrochemical transistors, micro- and nanofluidic lab-on-a-chip detection, and diverse
applications such as fuel cells and protein analysis.

Date: Friday 23 November 2018
Location: NH Hotel Groningen, Hanzeplein 132, 9713 GW Groningen

See here for the program, and here for the registration.

Publication: Electrochemical sensing with single nanoskived gold nanowires bisecting a microchannel

P. E. Oomen, Y. Zhang, R. C. Chiechi, E. Verpoorte and K. Mathwig, Lab on a Chip 18 (2018) 2913. [link, pdf]

toc_LC2We suspended a single nanoskived gold nanowire in a microfluidic channel. In this preliminary report, a 200-nm-diameter nanowire was used as an electrode to perform hydrodynamic voltammetry in the center of solution flow. Suspended nanowires exhibit superior current response due to highly efficient mass transport in the area of fastest flow.

Publication: Potential-Controlled Adsorption, Separation, and Detection of Redox Species in Nanofluidic Devices

Jin Cui, Klaus Mathwig, Dileep Mampallil and Serge G. Lemay, Analytical Chemistry 90 (2018) 7127. [link, pdf]

toc_chromatographyNanoscale channels and electrodes for electrochemical measurements exhibit extreme surface-to-volume ratios and a correspondingly high sensitivity to even weak degrees of surface interactions. Here, we exploit the potential-dependent reversible adsorption of outer-sphere redox species to modulate in space and time their concentration in a nanochannel under advective flow conditions. Induced concentration variations propagate downstream at a species-dependent velocity. This allows one to amperometrically distinguish between attomole amounts of species based on their time-of-flight. On-demand concentration pulse generation, separation, and detection are all integrated in a miniaturized platform.

Publication: Cationic diodes by hot-pressing of Fumasep FKS-30 ionomer film onto a microhole in polyethylene terephthalate (PET)

L. Tshwenya, O. Arotiba, B. R. Putra, E. Madrid, K. Mathwig and F. Marken, Journal of Electroanalytical Chemistry 815 (2018) 114. [link, pdf]

TOC_fumasepA cationic diode is fabricated by hot-pressing a commercial cation-conducting ionomer membrane (Fumasep FKS-30) onto a polyethylene terephthalate (PET) substrate with microhole of 5, 10, 20, or 40 μm diameter. Both, symmetric (ionomer on both sides) and asymmetric (ionomer only on the working electrode side) cases are investigated in a 4-electrode measurement cell. A 5-electrode measurement cell in generator-collector mode is employed to directly detect competing proton transport through the ionomer. Only the asymmetric device allows ion current rectification to be observed. With decreasing microhole diameter the rectification effect increases. With increasing electrolyte concentration (for aqueous HCl, NaCl, LiCl, NH4Cl, MgCl2, CaCl2) the rectification effect diminishes. Competition between cation transport and proton transport is observed in all cases. A qualitative impedance model is developed to diagnose the quality and performance of these cationic diodes.

Proceedings: An automated modular microsystem for enzymatic digestion with gut-on-a-chip applications

P. de Haan, M. A. Ianovska, K. Mathwig, H. Bouwmeester and E. Verpoorte, 21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, Savannah, Georgia, USA, Oct.  22-16 (2017) 1593.
[link, pdf]

Gut-on-a-chip models have gained attention as replacements for other cell-based assays or animal studies in drug development or toxicological studies. These models aim to provide a more accurate representation of the in vivo situation in form and function; however, no digestive processes have been included in these systems so far. This work describes a miniaturized digestive system based on artificial digestive juices that digest liquid samples in a series of three microreactors. After optimization of the pH value of juices and mixtures, samples leading to fluorescent products were digested to demonstrate enzyme functionality and to determine kinetic parameters.

Publication: Nano- and microgap electrochemical transducers: Novel benchtop fabrication techniques and electrical migration effects

F. Marken and K. Mathwig, Current Opinion in Electrochemistry, 7 (2018) 15. Themed Issue on Physical and Nanoelectrochemistry.
[link, pdf]

toccurrentopinRedox feedback mechanisms can be exploited in electroanalytical detection right to the limit of single molecules being observed. The process relies on anode and cathode being placed extremely close together to minimize diffusion time. In addition to the more complex and expensive nanofabrication tools, there are attempts of “benchtop” microgap and nanogap fabrication to exploit deposition and etch reactions in the assembly. An overview is given summarizing recent methodology development and emerging applications in electroanalysis. One important implication of a very close anode-to-cathode distance is migration of ions in a strong electric field when no electrolyte is used, leading to ion accumulation and a change in signal amplification. Phenomena of this type and geometry/functional implications are considered.

Preprint: Simple nanofluidic devices for high-throughput, non-equilibrium studies at the single-molecule level

C. Fijen, M. Fontana, S. G. Lemay, K. Mathwig and J. Hohlbein, bioRxiv (2017) 20179.

toc_biorxiv.pngSingle-molecule detection schemes offer powerful means to overcome static and dynamic heterogeneity inherent to complex samples. Probing chemical and biological interactions and reactions with high throughput and time resolution, however, remains challenging and often requires surface-immobilized entities. Here, utilizing camera-based fluorescence microscopy, we present glass-made nanofluidic devices in which fluorescently labelled molecules flow through nanochannels that confine their diffusional movement. The first design features an array of parallel nanochannels for high-throughput analysis of molecular species under equilibrium conditions allowing us to record 200.000 individual localization events in just 10 minutes. Using these localizations for single particle tracking, we were able to obtain accurate flow profiles including flow speeds and diffusion coefficients inside the channels.

Publication: Ionic Transport in Microhole Fluidic Diodes Based on Asymmetric Ionomer Film Deposits

K. Mathwig, B. D. B. Aaronson and F. Marken, ChemElectroChem 5 (2018) 897, Alan Bond Festschrift Special Issue (invited contribution).
[link, pdf]

Toc.pngMicrohole fluidic ionic diodes based on asymmetric deposits of charged ionomer membranes (e.g., Nafion or polymers of intrinsic microporosity) on microhole supports yield high rectification ratios for ionic transport. They are fabricated without the need for complex micro- or nano-structuring, and show potential for future applications in desalination and biosensing. Here, we propose an explanation for the functional principle for this type of materials-based ionic diode. A predictive computational model for ionic diode switching is based on finite element analysis. It is employed to determine the influence of diode geometry as well as type and concentration of aqueous electrolyte on the rectification behavior.

Publication: A Nanofluidic Mixing Device for High-Throughput Fluorescence Sensing of Single Molecules

K. Mathwig, C. Fijen, M. Fontana, S. G. Lemay and J. Hohlbein, Procedia Technology 27 (2017) 141.
[link, pdf]

procediatechnol_toc.pngWe introduce a nanofluidic mixing device entirely fabricated in glass for the fluorescence detection of single molecules. The design consists of a nanochannel T-junction and allows the continuous monitoring of chemical or enzymatic reactions of analytes as they arrive from two independent inlets. The fluorescently labeled molecules are tracked before, during and after they enter the mixing region, and their reactions with each other are observed by means of optical readout such as Förster Resonance Energy Transfer (FRET). Our method can be used for analyzing the kinetics of DNA annealing in a high-parallelized fashion.