Neuroendocrine tumors (NETs), often misdiagnosed andmistreated,require early detection for precise therapeutic interventions. Thisstudy presents a newly developed competitive electrochemical immunosensorfor sensitive and selective detection of chromogranin A (CgA), a keybiomarker for diagnosing and monitoring NETs. The sensor, featuringa sandwiched structure with versatile and multifunctional grapheneoxide (GO), utilizes polyethylenimine-capped gold nanoparticles (PEI-AuNPs)to enhance the electroreactivity and biocompatibility of a screen-printedelectrode (SPE). The immunosensor operates by immobilizing standardCgA antigens on the PEI-AuNPs/GO-modified SPE surface and employingGO nanotags loaded with anti-CgA antibodies (Ab) and ferrocene monocarboxylicacid (Fc) redox probes to capture target CgA. As the CgA concentrationincreases, the current response of the immunosensor decreases dueto a reduction in the amount of Fc/Ab/GO tags on the electrode surface.This reduction occurs because the nanotags bind to the free CgA inthe sample rather than the CgA immobilized on the electrode. The immunosensordemonstrates a good linearity (0.10–50 ng mL–1), a low detection limit of 90 pg mL–1, and highaccuracy in detecting CgA levels in human serum samples. With itshigh specificity, long-term stability, and excellent reproducibility,our cost-effective and user-friendly platform holds promise for clinicalscreening and point-of-care diagnosis of NETs. Further optimizationof the immunosensor’s design and exploration of its use foradditional biomarkers could enhance NETs’ diagnosis and provideadvancements in managing other related health conditions.

Repeated freezing and thawing (F-T) of meat, a commonpracticein home kitchens, markets, and transportation, reduces meat qualitydue to wide temperature fluctuations. This study presents the electrochemicalanalysis of oxidation in beef longissimus lumborum muscle sarcoplasmunder repeated F-T cycles, which differs from prior reports that focusedon other related meat aspects, such as discoloration, adulteration,freshness, and antibiotic detection. Moreover, comparing the complexityof meat extract analysis using certain spectral methods, such as Raman,NMR, FTIR, and expensive mass spectrometry, electrochemical methodsoffer simplicity, speed, and cost-effectiveness. Increased currentresponses at specific peaks (0.82 ± 0.01 V and −0.25 ±0.01 V vs Ag/AgCl) correlated strongly (r = 0.99, p < 0.01) with elevated metmyoglobin content, which isresponsible for the discoloration or brown color of meat, validatedby spectrophotometry. Frozen sarcoplasm (day 3) exhibited significantlyhigher currents and metmyoglobin levels (p < 0.01)compared to fresh sarcoplasm (day 0), indicating biochemical changesduring F-T cycles. Electrocatalytically accessed redox signals ofpurified beef myoglobin confirmed the contributions from the rapidoxidation of myoglobin, as well as other meat sarcoplasmic proteins.This research introduces a portable, cost-effective electrochemicaltool for point-of-need monitoring of meat oxidation under variouspractical, experimental, and environmental conditions. Future researchcould focus on obtaining insights into biochemical changes in longissimuslumborum sarcoplasm during frozen storage and developing strategiesto mitigate the effects of F-T cycles on meat quality.

In nanoscale sensors, understanding and predicting sensorsensitivityis challenging as the physical phenomena that govern the transductionmechanism are often highly nonlinear and highly coupled. The sensitivityof a sensor is related to both the magnitude of the analyte-causedsignal change and the random error-caused fluctuation of the sensor’soutput. The extent to which these can be controlled, by carefullydesigning either the geometric or operating conditions of the sensor,determines the difference in signal output between the presence andabsence of the analyte, as well as the impact of random errors onthe distribution of these signal outputs. Herein, we use ion-current-rectifyingnanopore sensors as a simplified case study to show how geometricand operating parameters can enable sensitivity optimization. Finiteelement analysis is used to obtain distributions of the sensor output,and then, Sobol analysis is used to highlight the most important contributionsto sensor output errors. Furthermore, the magnitude of the signalchange is considered alongside the spread of the output to calculateand optimize the sensor sensitivity. We highlight that the most importantparameters contributing to the output variance are geometric. We observedthat as the sensor is operated at smaller pore radii and lower electrolyteconcentrations, the influence of the cone angle errors increases,the influence of the pore radius errors decreases, and the outputbecomes broader. We also show that the highest sensitivity is expectedfor larger pores operated at low electrolyte concentrations, and oursimulation results are validated by experimental results. Recommendationsto achieve optimum sensitivity are given for a range of nanopore scenariosin which ion-rectifying nanopore sensors may be used. This work aimsto provide a framework for the nanoscale community to optimize sensitivityusing simulations, as the analysis highlighted herein is viable forany system that can be modeled using continuum physics.

Mass spectrometry (MS) has changed our understandingof health,disease, and the environment through untargeted analyses where entiremolecular classes are investigated. These techniques generate hugeamounts of data which when processed by statistical tools can identifyimportant molecular features or biomarkers. The complexities of thesesamples are not compatible with direct introduction to the MS systemand require a high-resolution separation step, typically low flowliquid chromatography (LC), prior to MS. LC columns that can produceadequate linear velocities at these low flow rates are small in volumemaking their results susceptible to resolution loss in extra-columnvolumes. Here, we investigate the implications of the extra-columneffects in five LC-MS systems with triple quadrupole and orbitrapmass analyzers. The extra-column volume of these systems in theirstandard configuration ranged from 26.4 to 78.1 μL which wereduced to 9.57 to 18.7 μL by optimizing the fluidics. The effectsof this volume reduction were assessed by studying a hydrolyzed proteinsample in a proteomics environment where the intensity of the largestMS peak was improved by 1.8–3.8×. Additionally, the numberof molecular features detected in the protein sample improved by upto 7.5×. The relationship between extra-column volumetric varianceand flow rate shows that broadening will become much larger for MSdetectors at higher flow rates, unlike a traditional small volumeUV detector. The methods, applications, and theoretical insights inthis work can be used to improve the mass spectrometric results ofany LC-MS system.

We investigated the influence of particle size on theelectrochemicalbehavior of Fe3O4 magnetite nanoparticles (MNPs)electrostatically adsorbed onto graphite electrodes modified witha preadsorbed poly­(ethylenimine) polycation layer. Three hydrodynamicsizes (50, 100, and 200 nm) were selected to assess size-dependentdifferences in electrochemical response using cyclic voltammetry underwell-controlled adsorption and measurement conditions. The 50 nm MNPsexhibited the highest electroactive response and peroxidase-like electrocatalyticcurrents, which are consistent with greater surface area-to-volumeratios. Qualitative image analysis from atomic force microscopy andscanning electron microscopy revealed closer particle spacing andmore extended surface contact for the smaller MNPs, in contrast toisolated aggregates formed by larger particles. These surface-leveldifferences were reflected in the electrochemical signals, where the50 nm particles yielded higher electroactive surface coverage. Thestudy demonstrates how particle size and interfacial organizationinfluence electrochemical readouts, underscoring the utility of correlatingmicroscopy with electrochemical data to evaluate nanoparticle-basedsensing interfaces.

Diabetes affectsover 8.8% of the global population, driving demandfor noninvasive glucose detection methods. Traditional enzymatic assaysare sensitive but face challenges such as high cost, complex preparation,low stability, and enzyme denaturation. This study aimed to enhanceglucose detection sensitivity with a noninvasive easy-to-use techniqueusing a fluorescent cellulose film. Lignin-derived carbon dots (LCDs)were synthesized as cost-effective, stable nanozymes for fluorescence-basedglucose sensing. It was found that doping noble metal Ru onto Pt/LCDssynthesized in water mimicked peroxidase enzyme and could enhancethe reactivity and sensitivity to ultralow levels for glucose detectionat room temperature. To fabricate a wearable sensor, a transparentcellulose film embedded with PtRu/LCDs and glucose oxidase (GOx) wasfabricated for biocompatible glucose sensing. The film achieved sensitivedetection in the range of 0.05–1.0 mM (R2 = 0.94) with a detection limit of 50 μM, suitable fornoninvasive glucose detection in saliva, tears, and sweat. This studyhighlights the potential of the PtRu/LCD-based cellulose film forhighly sensitive, wearable glucose sensors compatible with smartphoneapplications, offering a simple, real-time, noninvasive, fast, andchemical reagent-free glucose sensing for preventive healthcare.

Extracellular vesicles(EVs) are nanosized particles that are associatedwith various physiological and pathological functions. They play akey role in intercell communication and are used as transport vehiclesfor various cell components. In human milk, EVs are believed to beimportant for the development of acquired immunity. State-of-the-artanalysis methods are not able to provide label-free chemical informationat the single-vesicle level. We introduce a protocol to profile thestructure and composition of individual EVs with the help of atomicforce microscopy infrared spectroscopy (AFM-IR), a nanoscale chemicalimaging technique. The protocol includes the immobilization of EVsonto a silicon surface functionalized with anti-CD9 antibodies viamicrocontact printing. AFM-IR measurements of immobilized EVs providesize information and mid-infrared spectra at subvesicle spatial resolution.The received spectra compare favorably to bulk reference spectra.A key part of our protocol is a technique to acquire spectral informationabout a large number of EVs through hyperspectral imaging combinedwith image processing to correct for image drift and select individualvesicles.

We report mapping the mechanical properties of humanred bloodcells at submicron scales. Mapping is achieved via a new approachto scanning ion conductance microscopy correlated with optical microscopy.A three-point calibration and affine transformation are utilized tocorrelate pixel locations registered in optical images with pipetteposition, which facilitates initial targeting and subsequent trackingand analysis of red blood cells. By recording the response of pipetteapproach curves and sample compliance at each approach, maps of theYoung’s modulus of samples and pipette indentation are recordedat subcellular spatial resolution. Comparison of normal and diamide-treatedred blood cells shows a significant increase in cell stiffness anda concomitant decrease in deformability, clearly demonstrating thequantitative abilities of the correlative approach taken here forstiffness measurements of intact cellular samples.