ImportanceBreath analysis has been explored as a noninvasive means to detect COVID-19. However, the impact of emerging variants of SARS-CoV-2, such as Omicron, on the exhaled breath profile and diagnostic accuracy of breath analysis is unknown.ObjectiveTo evaluate the diagnostic accuracies of breath analysis on detecting patients with COVID-19 when the SARS-CoV-2 Delta and Omicron variants were most prevalent.Design, Setting, and ParticipantsThis diagnostic study included a cohort of patients who had positive and negative test results for COVID-19 using reverse transcriptase polymerase chain reaction between April 2021 and May 2022, which covers the period when the Delta variant was overtaken by Omicron as the major variant. Patients were enrolled through intensive care units and the emergency department at the University of Michigan Health System. Patient breath was analyzed with portable gas chromatography.Main Outcomes and MeasuresDifferent sets of VOC biomarkers were identified that distinguished between COVID-19 (SARS-CoV-2 Delta and Omicron variants) and non–COVID-19 illness.ResultsOverall, 205 breath samples from 167 adult patients were analyzed. A total of 77 patients (mean [SD] age, 58.5 [16.1] years; 41 [53.2%] male patients; 13 [16.9%] Black and 59 [76.6%] White patients) had COVID-19, and 91 patients (mean [SD] age, 54.3 [17.1] years; 43 [47.3%] male patients; 11 [12.1%] Black and 76 [83.5%] White patients) had non–COVID-19 illness. Several patients were analyzed over multiple days. Among 94 positive samples, 41 samples were from patients in 2021 infected with the Delta or other variants, and 53 samples were from patients in 2022 infected with the Omicron variant, based on the State of Michigan and US Centers for Disease Control and Prevention surveillance data. Four VOC biomarkers were found to distinguish between COVID-19 (Delta and other 2021 variants) and non–COVID-19 illness with an accuracy of 94.7%. However, accuracy dropped substantially to 82.1% when these biomarkers were applied to the Omicron variant. Four new VOC biomarkers were found to distinguish the Omicron variant and non–COVID-19 illness (accuracy, 90.9%). Breath analysis distinguished Omicron from the earlier variants with an accuracy of 91.5% and COVID-19 (all SARS-CoV-2 variants) vs non–COVID-19 illness with 90.2% accuracy.Conclusions and RelevanceThe findings of this diagnostic study suggest that breath analysis has promise for COVID-19 detection. However, similar to rapid antigen testing, the emergence of new variants poses diagnostic challenges. The results of this study warrant additional evaluation on how to overcome these challenges to use breath analysis to improve the diagnosis and care of patients.

MXene's two-dimensional (2D) morphology, metallic electrical conductivity, and optical transparency characteristics have been widely utilized to uplift the performance of diverse optoelectronic devices. In this study, we demonstrate a simple spin-coating of 2D MXene nanosheets on 1D GaN nanorods (NRs) to establish a van der Waals (vdW) Schottky junction, which is efficient to detect UV radiation (λ = 382 nm) without requiring the external power supply. The built-in electric field developed through vdW Schottky junction formation stimulates the separation of electron–hole pairs and thereby facilitates the MXene/GaN NRs device to exhibit better UV detection performance than the pristine GaN NRs device. The performance of both pristine GaN and MXene/GaN NRs devices is compared by tuning the UV radiation power density in the range of 0.33–1.35 mW/cm2. Notably, the self-powered MXene/GaN NRs photodetector demonstrated the characteristics of high photoresponsivity (48.6 mA/W), detectivity (5.9 [Formula: see text] 1012 Jones), and external quantum efficiency (543%). These characteristics signify the suitability of MXene/GaN self-powered photodetectors for various applications, including imaging, sensing networks, and energy-saving communication.

Although gallium nitride (GaN) nanostructures are auspicious for photocatalytic activity, geometrical optimization has paid much attention for a significant light trapping in photoelectrochemical applications. To minimize the optical losses, we designed a prototype V-groove textured Si (100) with (111) facets, and GaN nanorods (NRs) were grown over a prototype substrate using plasma-assisted molecular beam epitaxy. The photocurrent density of V-groove textured GaN NRs in the NaOH electrolyte is found to be 801.62 μA/cm2 at 1.14 V vs reversible hydrogen electrode, which was 2.1-fold larger than that of GaN NRs on plain Si (111). Using this prototype V-groove textured Si(100) with (111) facets, a significant light can be trapped and modulated into GaN NRs. Furthermore, the heterostructure between GaN NRs and V-groove textured Si stimulates effective charge separation and transportation. These results represent an important forward step in solar photoelectrolysis.

Materials with peculiar nanostructures enclosing the surface play a pivotal role in a variety of applications, especially gas-sensing applications, due to their high surface-to-volume ratio. In this study, we tailored the nanorod (NR) morphology of InGaN into various unusual shapes such as bud, mace, and feather shapes and investigated the gas-sensing abilities of these structures. Remarkably, tuning the NR morphology significantly enhanced the NO2 gas response, with the feather-shaped morphology showing the best performance. The feather-shaped InGaN NRs displayed a response of 72.64% to 100 ppm NO2 gas, which is not only four times that of pristine InGaN NRs but also the highest response so far compared to that among state-of-the-art InGaN- or GaN-based NO2 gas sensors. Furthermore, photon-assisted sensing stimulated the responses of feather-shaped InGaN NRs, with the limit of detection extending to 200 ppb (6.12%). In addition, feather-shaped InGaN NRs were more selective to NO2 gas than to other target gases such as H2S, H2, NH3, and CO. The growth mechanisms of the different morphologies, as well as their enhanced NO2 gas responses, were successfully demonstrated. This morphology engineering strategy can be extended to design III-nitrides of different shapes for excellent gas-sensing applications.