Electrical sensing technologies have advanced our abilityto inferand evaluate the hydraulic characteristics of porous media that areotherwise inaccessible to direct measurement. Such challenges areparticularly prevalent in geo-porous materials such as rocks and soilsfound in remote regions, harsh environments, or beneath the Earth’ssurface. Noninvasive sensing and characterization of these materialsare indispensable preliminary steps for water–energy nexusactivities, including extraction processes (e.g., desalination, groundwaterutilization, fossil fuel and geothermal exploration and production)and mitigation efforts (e.g., sediment transport monitoring, contaminantmanagement, and carbon or hydrogen capture, utilization, and storage).These electrical properties are measurable only if the material underinvestigation possesses an electrical charge and is polarizable. Electricalpolarization refers to the relative displacement between positiveand negative charges. This raises several critical questions: (i)In what ways can porous media acquire electrical charge and exhibitpolarization? (ii) How can their electrical properties be measuredboth in laboratory and field environments? (iii) What frameworks canbe used to interpret the observed electrical properties? (iv) Howcan we assess the reliability and validity of these interpretationsin relation to the hydraulic and physical state of the porous media?This study aims to systematically investigate these questions througha comprehensive synthesis of existing literature and the integrationof newly obtained experimental data.

The expanding use of microfluidic droplets and particlesacrossdisciplines, from biology to materials science, highlights the needfor developing precise characterization methods. Conventional particlecharacterization based on light scattering typically relies on averageddata from multiple particles, which can lead to inaccuracies due tocontamination from larger particles. To overcome this issue, we herepresent a versatile laser diffraction (LD) system for characterizingindividual droplets and particles flowing in a poly­(dimethylsiloxane)(PDMS) microfluidic device. Our system, mounted on a commercial invertedmicroscope, facilitates the simultaneous estimation of both the diameterand the refractive index of microparticles and droplets of size 20–50μm. The LD system captures the angular distribution of scatteredlight from individual droplets as they pass through the PDMS microfluidicchannels. Validation experiments were performed using liquid paraffinwith varying refractive indices, oil-in-water (O/W) and water-in-oil(W/O) droplets, and size-certified polystyrene beads. Results showedhigh accuracy, with mean diameter estimation errors under 5% and refractiveindex estimation errors <0.5%. This adaptable characterizationsystem can be combined with various microfluidic systems for dropletand particle generation, mixing, and sorting, offering broad potentialfor applications in multiple research domains.

Ex vivo tissue culture can model tissuephysiologyunder well-controlled conditions and is especially promising for understandingthe complex mechanisms of the brain. Three-dimensional (3D) printinghas immense potential to accelerate microfluidic technology development,especially for ex vivo tissue culture devices whereminiaturization is ultimately limited by the physical dimensions oftissue explants. Here we describe the development of a 3D printedmicrofluidic perfusion device for ex vivo brain slicesthat utilizes media droplets segmented by oxygen bubbles, a perfusiontechnique we call “bubble perfusion”. Device designconsiderations are described, including materials property challengesassociated with 3D printed plastic, such as wetting behavior and thermalconductivity challenges. Integrating a heated water circulation chamberand media prewarming chambers yielded media droplets delivered tobrain slice explants at a temperature of 36.8 ± 0.13 °C,with tissue experiencing a temperature drift of 0.5 ± 0.09 °Cover the course of a 60 s media droplet exposure. Murine brain tissueexplants containing the suprachiasmatic nucleus (SCN) or entorhinalcortex (EC) were observed to be viable within the perfusion systemby fluorescence imaging of intracellular Ca2+ flux inducedby single-droplet stimulus of 60 mM KCl. Robust Ca2+ fluxwas observed for perfusion experiments lasting up to 12 h, with sequentialdroplet observations indicating the temporal dynamics of Ca2+ responses. End-point propidium iodide staining was used to characterizethe health of EC and SCN tissue, with ca. 60% ofcells in both regions showing no sign of membrane damage after 12h of perfusion. The utility of the perfusion system toward pharmacologicalstudies was demonstrated by comparing the Ca2+ flux inducedby stimulus with 50 μM cannabidiol (CBD) vs 50 μM anandamide (AEA). Interestingly, similar magnitude andtemporal dynamics of Ca2+ flux were observed for both CBDand AEA stimuli despite differential proposed mechanisms of actionwith respect to the CB1 receptor. These studies demonstrate the utilityof the 3D printed bubble perfusion system toward the study of receptor-bindingligands that induce relatively modest magnitudes of Ca2+ flux.

Microbial detection techniques, such as bacterial counting,areessential in all aspects of environmental monitoring and analysis.However, the standard plate count method for bacterial enumerationwith colony-forming units is time-consuming and labor-intensive. Inthis study, we present a fast and accurate method to count bacteriacells using the technique of time-domain reflectometry (TDR) basedon the electrical properties of bacterial cell suspensions. A seriesof suspensions with various bacterial concentrations were used asthe test materials, and the electrical conductivity (σa) was determined using the TDR method. The TDR measured-σa value was converted to the concentration of bacterial suspensionusing a pre-established standard curve on three types of bacteria,i.e., Bacillus subtilis (B. subtilis), Pseudomonas fluorescens (P. fluorescens), and Escherichia coli (E. coli). The σa values of suspensions increased exponentiallywith bacteria concentrations, mainly due to the release of Cl– and extracellular polymeric substances from the cellsthat were electrically conductive. For the three types of bacterialstrains, the lower detection limits were 6 log CFU mL–1 for B. subtilis, and 7 log CFU mL–1 for P. fluorescens and E. coli. Independent evaluationshowed that values from the TDR based method matched well with thoseobtained with the traditional plate count method, with RMSEs of 0.260,0.166, and 0.198 log CFU mL–1 for B. subtilis, P. fluorescens, and E. coli, respectively. The TDRbased approach provides a fast and accurate means for detecting bacterialcell numbers in suspensions.

The reliability of the Tauc plot method for estimatinga material’soptical bandgap critically depends on the accurate quantificationof its absorption coefficient (α), defined as the path length–normalizedabsorbance. This study systematically evaluates and compares threespectroscopic techniques, ultraviolet–visible (UV–vis)spectroscopy, diffuse reflectance spectroscopy (DRS), and integratingsphere-assisted resonance synchronous spectroscopy (ISARS), for theireffectiveness in determining the absorption coefficient spectrum usedin Tauc plot–based bandgap analysis. For each technique, ageneralized mathematical model is developed by parametrizing the measuredspectral signal as a functional expression of the sample’soptical properties and experimental conditions. These models providea conceptual framework under which the measured spectra can reliablyapproximate the true absorption coefficient spectrum, particularlyfor materials with diverse optical behaviors. UV–vis spectroscopyis found to have highly limited applicability and is suitable onlyin rare cases where samples are free from scattering and fluorescenceinterference. While DRS and ISARS yield comparable accuracy for nonfluorescentsolids, DRS is constrained by its sensitivity to fluorescence artifactsand its restriction to solid-state samples. In contrast, ISARS consistentlyoutperforms both methods: it is effective for both solid- and solution-phasesamples, demonstrates strong resilience against scattering and fluorescenceinterference, and requires minimal sample preparation. Importantly,ISARS can be readily implemented by using a standard commercial spectrofluorometerequipped with an integrating sphere, making it both practical andaccessible. Given its superior accuracy, broad applicability, andease of use, ISARS stands out as a robust and versatile techniquefor precise bandgap characterization, offering significant promisefor accelerating the discovery and development of photoactive materials.

Chemometrics associated with advanced analytical separationmethodsare crucial for the chemical profiling of complex samples, such asbio-oil, enabling more accurate and efficient identification of differentialfeatures. The composition of bio-oils influences the selection ofpretreatment methods for fuel production, which may include processessuch as filtration, guard bed usage, or reactions such as hydrothermalliquefaction and esterification. This study focuses on the chemicalprofiling of pyrolytic bio-oils from sugar cane bagasse and strawusing comprehensive two-dimensional gas chromatography coupled withtime-of-flight mass spectrometry (GC×GC-TOFMS). Chemometric approachessuch as tile-based Fisher ratio analysis (FRA) and principal componentanalysis (PCA) are employed for the feature selection of class-differentiatinganalytes. Bio-oils from both feedstocks exhibited chromatographicprofiles with subtle differences, which were observed in the compositionand relative abundance of specific compound classes. Bagasse bio-oilwas rich in phenolics and hexose derivatives, such as furans and aldehydes.In contrast, straw bio-oil presented a higher abundance of hydrocarbonsand fatty acid methyl esters. Tile-based FRA enabled the identificationof 16 differential features and the detection of low-intensity compounds,such as long-chain esters and hydrocarbons, not previously detectedby the peak table-based approach. PCA based on these differentialfeatures explained 98.7% of the total variance (PC1 + PC2), clearlygrouping bio-oils by feedstock origin. The findings highlight thepotential of GC×GC-TOFMS and chemometrics for differentiatingbio-oils, demonstrating the importance of advanced analytical techniquesin studying biomass conversion processes and characterizing bioproducts.

Results of efforts to diagnose infections with SARS-CoV-2usinga sampling method that was less invasive than the nasopharyngeal swabled to the rapid adoption of anterior nasal swabs. Saliva was alsoshown to have potential as a sample matrix and, like anterior nasalswabs, could be obtained noninvasively (e.g., passive drool). However,due to its inherent complexity and heterogeneity across patient populations(e.g., presence of mucins and RNases), saliva was largely disregardedas point-of-care diagnostics were being developed and broadly implemented.For molecular diagnostic approaches (e.g., RT-PCR or RT-LAMP), thesematrix effects from saliva could lead to undesirable false positivesor false negatives. The opportunity to address these challenges bynormalizing the performance of saliva could enable important applicationsof molecular tests, particularly at the point-of-care. Toward thesegoals, we developed a one-pot RT-LAMP assay for the colorimetric detectionof SARS-CoV-2 from saliva samples. The assay is performed in fivesteps: (i) a patient collects a passive saliva sample, (ii) the sampleis placed on a heat block for 10 min at 95 °C, (iii) the undilutedsample is added to the one-pot RT-LAMP assay, (iv) the RT-LAMP reactiontube is place on a heat block for 40 min at 65 °C, and, (v) immediatelypostamplification, the reaction tube is inverted to observe the colorimetricoutput. We demonstrated the clinical performance of our assay usinga panel of 127 patient samples. Our assay had an overall accuracyof 98%, with a sensitivity of 88% and a specificity of 100%. Theseresults indicate excellent diagnostic agreement with the gold standard,RT-PCR, and highlight the potential to improve the clinical utilityof saliva for point-of-care (e.g., mobile clinics) testing of SARS-CoV-2and other upper respiratory viruses and emerging pathogens.

Measuring surfacefunctional groups (FGs) on nanomaterials (NMs)is essential for designing dispersible and stable NMs with tailoredand predictable functionality. FG screening and quantification alsoplays a critical role for subsequent processing steps, NM long-termstability, quality control of NM production, and risk assessment studiesand enables the implementation of sustainable and safe­(r)-by-designconcepts. This calls for simple and cost-efficient methods for broadlyutilized FGs that can be ideally automated to speed up FG screening,monitoring, and quantification. To expand our NM surface analysistoolbox, focusing on simple methods and broadly available, cost-efficientinstrumentation, we explored a NM-adapted pH titration method withpotentiometric and optical readout for measuring the total numberof (de)­protonable FGs on representatively chosen commercial and custom-madeaminated silica nanoparticles (SiO2 NPs). The accuracyand robustness of our stepwise optimized workflows was assessed byseveral operators in two laboratories and method validation was doneby cross-comparison with two analytical methods relying on differentsignal generation principles. This included traceable, chemo-selectivequantitative nuclear magnetic resonance spectroscopy (qNMR) and thermogravimetricanalysis (TGA), providing the amounts of amino silanes released byparticle dissolution and the total mass of the surface coatings. Acomparison of the potentiometric titration results with the reporter-specificamounts of surface amino FGs determined with the previously automatedfluorescamine (Fluram) assay highlights the importance of determiningboth quantities for surface-functionalized NMs. In the future, combinedNM surface analysis with optical assays and pH titration will simplifyquality control of NM production processes and stability studies andcan yield large data sets for NM grouping that facilitates furtherdevelopments in regulation and standardization.

Human milk oligosaccharides (HMOs) are a biologicallyimportantclass of carbohydrates responsible for promoting the healthy developmentof infants. However, to better understand their specific biologicalroles, analytical techniques are needed to unambiguously characterizethem. While liquid chromatography–tandem mass spectrometry(LC-MS/MS) remains the gold standard for HMO analysis, new orthogonaltechniques are desired for improving their isomer analysis. Ion mobilityspectrometry–mass spectrometry (IMS-MS) has emerged as a complementarytechnique to LC-MS/MS but has seen little use toward HMO sequencinganalysis beyond the construction of collision cross section (CCS)databases. In this work, we describe the use of collision-induceddissociation performed prior to high-resolution cyclic ion mobilityseparations (i.e., pre-cIMS CID) in conjunction with CCS measurementsto characterize the linkage positioning in various HMOs irrespectiveof the starting precursor ion. We then demonstrated how our developedapproach could be used to sequence an unknown HMO present in a purifiedextract. Lastly, we applied our workflow to sequence an isomeric mixturein the same extract using cIMS/cIMS instead of pre-cIMS CID. Overall,our developed approach is a first step toward standard-free de novo HMO sequencing as well as being a complementaryand orthogonal method to existing LC-MS/MS-based workflows.

Accurate and rapid analysis of chirality is crucial forunderstandingbiological processes and molecular interactions, yet traditional vibrationalcircular dichroism (VCD) techniques are limited by long acquisitiontimes and low throughput. We present a quantum cascade laser (QCL)-basedVCD system that integrates a photoelastic modulator (PEM) with pulsedlaser sources, using precise temporal synchronization and a novelcalibration method based on Welch’s power spectral densityanalysis. This hardware-software integration enables real-time demodulationwithout the need for conventional lock-in amplifiers and achievesaccurate, high-SNR VCD spectra of α-pinene (±) mixtureswith high reproducibility. Real-time enantiomeric excess determinationis achieved with a 10× improvement in speed and a 5× enhancementin SNR compared to conventional VCD methods. These advancements pavethe way for high-throughput and nondestructive chiral analysis, withpotential applications in biosensing, structural biology, and pharmaceuticalresearch.