Integrated impedance sensing of liquid sample plug flow enables automated high throughput NMR spectroscopy

A novel approach for automated high throughput NMR spectroscopy with improved mass-sensitivity is accomplished by integrating microfluidic technologies and micro-NMR resonators.A flow system is utilized to transport a sample of interest from outside the NMR magnet through the NMR detector,circumventing the relatively vast dead volume in the supplying tube by loading a series of individual sample plugs separated by an immiscible fluid.This dual-phase flow demands a real-time robust sensing system to track the sample position and velocities and synchronize the NMR acquisition.In this contribution,we describe an NMR probe head that possesses a microfluidic system featuring:(i)a micro saddle coil for NMR spectroscopy and(ii)a pair of interdigitated capacitive sensors flanking the NMR detector for continuous position and velocity monitoring of the plugs with respect to the NMR detector.The system was successfully tested for automating flow-based measurement in a 500 MHz NMR system,enabling high resolution spectroscopy and NMR sensitivity of 2.18 nmol s1/2 with the flow sensors in operation.The flow sensors featured sensitivity to an absolute difference of 0.2 in relative permittivity,enabling distinction between most common solvents.It was demonstrated that a fully automated NMR measurement of nine individual 120μL samples could be done within 3.6 min or effectively 15.3 s per sample.

Laser-induced hierarchical carbon patterns on polyimide substrates for flexible urea sensors

Thermochemical decomposition of organic materials under heat-treatment in the absence of oxygen,known as the pyrolysis process,is often employed to convert micro and nano patterned polymers into carbon structures,which are subsequently used as device components.Pyrolysis is performed at≥900℃,which entails substrate materials with a high thermal stability that excludes flexible,polymeric substrates.We use optimized laser radiation to pattern graphitic carbon structures onto commercially available polyimide(Kapton)sheets in the micrometer to millimeter scale by inducing a localized,rapid pyrolysis,for the fabrication of flexible devices.Resulting laser carbon films are electrically conductive and exhibit a high-surface area with a hierarchical porosity distribution along their cross-section.The material is obtained using various combinations of laser parameters and pyrolysis environment(oxygen-containing and inert).Extensive characterization of laser carbon is performed to understand the correlation between the material properties and laser parameters,primarily fluence and power.A photothermal carbonization mechanism based on the plume formation is proposed.Further,laser carbon is used for the fabrication of enzymatic,pH-based urea sensors using two approaches:(i)direct urease enzyme immobilization onto carbon and(ii)electrodeposition of an intermediate chitosan layer prior to urease immobilization.This flexible sensor is tested for quantitative urea detection down to 10^(−4) M concentrations,while a qualitative,color-indicative test is performed on a folded sensor placed inside a tube to demonstrate its compatibility with catheters.Laser carbon is suitable for a variety of other flexible electronics and sensors,can be conveniently integrated with an external circuitry,heating elements,and with other microfabrication techniques such as fluidic platforms.