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1. A microfluidic electrochemical flow cell capable of rapid on-chip dilution for fast-scan cyclic voltammetry electrode calibration

   https://doi.org/10.1007/s00216-020-02493-z  

   Delong, Lauren M.; Li, Yuxin; Lim, Gary N.; Wairegi, Salmika G.; Ross, Ashley E. (February 2020, Analytical and Bioanalytical Chemistry)

   Here, we developed a microfluidic electrochemical flow cell for fast-scan cyclic voltammetry which is capable of rapid on-chip dilution for efficient and cost-effective electrode calibration. Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes is a robust electroanalytical technique used to measure subsecond changes in neurotransmitter concentration over time.Traditional methods of electrode calibration for FSCV require several milliliters of a standard. Additionally, generating calibration curves can be time-consuming because separate solutions must be prepared for each concentration. Microfluidic electrochemical flow cells have been developed in the past; however, they often require incorporating the electrode in the device, making it difficult to remove for testing in biological tissues. Likewise, current microfluidic electrochemical flow cells are not capable of rapid on-chip dilution to eliminate the requirement of making multiple solutions. We designed a T-channel device, with microchannel dimensions of 100 μm × 50 μm, that delivered a standard to a 2-mm-diameter open electrode sampling well. A waste channel with the same dimensions was designed perpendicular to the well to flush and remove the standard. The dimensions of the T-microchannels and flow rates were chosen to facilitate complete mixing in the delivery channel prior to reaching the electrode. The degree of mixing was computationally modeled using COMSOL and was quantitatively assessed in the device using both colored dyes and electrochemical detection. On-chip electrode calibration for dopamine with FSCV was not significantly different than the traditional calibration method demonstrating its utility for FSCV calibration. Overall, this device improves the efficiency and ease of electrode calibration. 

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2. Isotopic N,N-Dimethyl Leucine-Based Mass Spectrometric Quantification of Metabolites Following Copper Exposure

   https://doi.org/10.3390/biom15091264  

   Riusech, Olga; Li, Lingjun (September 2025, Biomolecules)

   Crustaceans are particularly sensitive to copper toxicity, and although the downstream effects of increased copper exposure on the metabolome are often postulated and observed, they are rarely measured. To perform absolute quantification of hydrophilic small-molecule metabolites in the hemolymph of the crustacean Cancer borealis, we derivatized targeted metabolites related to copper toxicity using in-house-developed isotopic N,N-dimethyl leucine (iDiLeu) tags. Selected analytes were pooled at previously determined concentrations to serve as internal standards, and a calibration curve was generated. The sample loss was minimized by optimizing the derivatization-assisted sample cleanup using dispersive liquid–liquid microextraction (DLLME) and hydrophilic–lipophilic balancing (HLB). Calibration curves were then used for the absolute quantification of metabolites of interest following 30 min, 1 h, and 2 h exposures to 10 µM CuCl2. We found that glutamic acid was downregulated after 2 h of copper exposure, which may disrupt cellular metabolism and increase oxidative stress in crustaceans. These changes could have significant impacts on crustacean populations and the ecosystems they support. 

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3. Dean vortex-enhanced blood plasma separation in self-driven spiral microchannel flow with cross-flow microfilters

   https://doi.org/10.1063/5.0189413  

   Wang, Yudong; Talukder, Niladri; Nunna, Bharath Babu; Lee, Eon Soo (February 2024, Biomicrofluidics)

   Point-of-care (POC) diagnostic devices have been developing rapidly in recent years, but they are mainly using saliva instead of blood as a test sample. A highly efficient self-separation during the self-driven flow without power systems is desired for expanding the point-of-care diagnostic devices. Microfiltration stands out as a promising technique for blood plasma separation but faces limitations due to blood cell clogging, resulting in reduced separation speed and efficiency. These limitations are mainly caused by the high viscosity and hematocrit in the blood flow. A small increment in the hematocrit of the blood significantly increases the pressure needed for the blood plasma separation in the micro-filters and decreases the separation speed and efficiency. Addressing this challenge, this study explores the feasibility of diluting whole blood within a microfluidic device without external power systems. This study implemented a spiral microchannel utilizing the inertial focusing and Dean vortex effects to focus the red blood cells and extract the blood with lower hematocrit. The inertial migration of the particles during the capillary flow was first investigated experimentally; a maximum of 88% of the particles migrated to the bottom and top equilibrium positions in the optimized 350 × 60 μm (cross-sectional area, 5.8 aspect ratio) microchannel. With the optimized dimension of the microchannel, the whole blood samples within the physiological hematocrit range were tested in the experiments, and more than 10% of the hematocrit reduction was compared between the outer branch outlet and inner branch outlet in the 350 × 60 μm microchannel. 

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4. An Empirical Evaluation of the Calibration of Auditory Distance Perception under Different Levels of Virtual Environment Visibilities

   https://doi.org/10.1109/VR58804.2024.00089  

   Lin, Wan-Yi; Venkatakrishnan, Rohith; Venkatakrishnan, Roshan; Babu, Sabarish V; Pagano, Christopher; Lin, Wen-Chieh (March 2024, IEEE)

   The perception of distance is a complex process that often involves sensory information beyond that of just vision. In this work, we investigated if depth perception based on auditory information can be calibrated, a process by which perceptual accuracy of depth judgments can be improved by providing feedback and then performing corrective actions. We further investigated if perceptual learning through carryover effects of calibration occurs in different levels of a virtual environment’s visibility based on different levels of virtual lighting. Users performed an auditory depth judgment task over several trials in which they walked where they perceived an aural sound to be, yielding absolute estimates of perceived distance. This task was performed in three sequential phases: pretest, calibration, posttest. Feedback on the perceptual accuracy of distance estimates was only provided in the calibration phase, allowing to study the calibration of auditory depth perception. We employed a 2 (Visibility of virtual environment) ×3 (Phase) ×5 (Target Distance) multi-factorial design, manipulating the phase and target distance as within-subjects factors, and the visibility of the virtual environment as a between-subjects factor. Our results revealed that users generally tend to underestimate aurally perceived distances in VR similar to the distance compression effects that commonly occur in visual distance perception in VR. We found that auditory depth estimates, obtained using an absolute measure, can be calibrated to become more accurate through feedback and corrective action. In terms of environment visibility, we find that environments visible enough to reveal their extent may contain visual information that users attune to in scaling aurally perceived depth. 

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5. Potentiometric Sensor System with Self-Calibration for Long-Term, In Situ Measurements

   https://doi.org/10.3390/chemosensors11010048  

   Zhang, Zhehao; Boselli, Elena; Papautsky, Ian (January 2023, Chemosensors)

   We built an integrated solid-contact ion-selective electrode (SCISE) system with the functionality of self-calibration. A multiplexed SCISE sensor (K+ and NO3− vs. Ag/AgCl) was fabricated on printed-circuit board (PCB) substrates and was subsequently embedded into a microfluidic flow cell for self-calibration and flow-through analysis. A PCB circuit that includes modules for both sensor readout and fluid control was developed. The sensors showed a fast and near-Nernstian response (56.6 for the K+ electrode and −57.4 mV/dec for the NO3− electrode) and maintained their performance for at least three weeks. The sensors also showed a highly reproducible response in an automated two-point calibration, demonstrating the potential for in situ monitoring. Lastly, the sensor system was successfully applied to measure mineral nutrients in plant sap samples. 

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