On-Site Quantification and Infection Risk Assessment of Airborne SARS-CoV-2 Virus Via a Nanoplasmonic Bioaerosol Sensing System in Healthcare Settings

On-site quantification and early-stage infection risk assessment of airborne severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with high spatiotemporal resolution is a promising approach for mitigating the spread of coronavirus disease 2019 (COVID-19) pandemic and informing life-saving decisions. Here, a condensation (hygroscopic growth)-assisted bioaerosol collection and plasmonic photothermal sensing (CAPS) system for on-site quantitative risk analysis of SARS-CoV-2 virus-laden aerosols is presented. The CAPS system provided rapid thermoplasmonic biosensing results after an aerosol-to-hydrosol sampling process in COVID-19-related environments including a hospital and a nursing home. The detection limit reached 0.25 copies/µL in the complex aerosol background without further purification. More importantly, the CAPS system enabled direct measurement of the SARS-CoV-2 virus exposures with high spatiotemporal resolution. Measurement and feedback of the results to healthcare workers and patients via a QR-code are completed within two hours. Based on a dose-responseµ model, it is used the plasmonic biosensing signal to calculate probabilities of SARS-CoV-2 infection risk and estimate maximum exposure durations to an acceptable risk threshold in different environmental settings

Recent Development of Optofluidics for Imaging and Sensing Applications

Optofluidics represents the interaction of light and fluids on a chip that integrates microfluidics and optics, which provides a promising optical platform for manipulating and analyzing fluid samples. Recent years have witnessed a substantial growth in optofluidic devices, including the integration of optical and fluidic control units, the incorporation of diverse photonic nanostructures, and new applications. All these advancements have enabled the implementation of optofluidics with improved performance. In this review, the recent advances of fabrication techniques and cutting-edge applications of optofluidic devices are presented, with a special focus on the developments of imaging and sensing. Specifically, the optofluidic based imaging techniques and applications are summarized, including the high-throughput cytometry, biochemical analysis, and optofluidic nanoparticle manipulation. The optofluidic sensing section is categorized according to the modulation approaches and the transduction mechanisms, represented by absorption, reflection/refraction, scattering, and plasmonics. Perspectives on future developments and promising avenues in the fields of optofluidics are also provided

Recent Development of Optofluidics for Imaging and Sensing Applications

Optofluidics represents the interaction of light and fluids on a chip that integrates microfluidics and optics, which provides a promising optical platform for manipulating and analyzing fluid samples. Recent years have witnessed a substantial growth in optofluidic devices, including the integration of optical and fluidic control units, the incorporation of diverse photonic nanostructures, and new applications. All these advancements have enabled the implementation of optofluidics with improved performance. In this review, the recent advances of fabrication techniques and cutting-edge applications of optofluidic devices are presented, with a special focus on the developments of imaging and sensing. Specifically, the optofluidic based imaging techniques and applications are summarized, including the high-throughput cytometry, biochemical analysis, and optofluidic nanoparticle manipulation. The optofluidic sensing section is categorized according to the modulation approaches and the transduction mechanisms, represented by absorption, reflection/refraction, scattering, and plasmonics. Perspectives on future developments and promising avenues in the fields of optofluidics are also provided

Recent Development of Optofluidics for Imaging and Sensing Applications

Optofluidics represents the interaction of light and fluids on a chip that integrates microfluidics and optics, which provides a promising optical platform for manipulating and analyzing fluid samples. Recent years have witnessed a substantial growth in optofluidic devices, including the integration of optical and fluidic control units, the incorporation of diverse photonic nanostructures, and new applications. All these advancements have enabled the implementation of optofluidics with improved performance. In this review, the recent advances of fabrication techniques and cutting-edge applications of optofluidic devices are presented, with a special focus on the developments of imaging and sensing. Specifically, the optofluidic based imaging techniques and applications are summarized, including the high-throughput cytometry, biochemical analysis, and optofluidic nanoparticle manipulation. The optofluidic sensing section is categorized according to the modulation approaches and the transduction mechanisms, represented by absorption, reflection/refraction, scattering, and plasmonics. Perspectives on future developments and promising avenues in the fields of optofluidics are also provided

A 3D-cascade-microlens optofluidic chip for refractometry with adjustable sensitivity†

Refractive index (RI) sensing as a label-free and non-invasive method has been playing an important role in industrial metrology, biochemical detection, and environmental analysis. Due to the combined advantages of microoptics and microfluidics, optofluidic RI sensors have attracted growing interest. Despite a variety of prototypes of optofluidic RI sensors, comprehensive improvement in sensitivity, detection range, fabrication procedures and cost can still bring substantial benefits to the field. In this work, we fabricated a 3D-cascade-microlens optofluidic chip (3DCMOC) for RI sensing. Two-photon stereolithography was employed to fabricate the chip mold, with which the 3DCMOC could be easily manufactured via mold replication. By virtue of integrating four detection channels configured with different numbers (1, 3, 5, and 7) of cascaded microlenses within the 3DCMOC, adjustable sensitivity for RI sensing has been demonstrated through measuring standard sucrose solutions. It was found that the seven-microlens configuration achieved an excellent sensitivity (mean: 21 ± 5 AU·RIU (refractive index unit)−1) and resolution (mean: 3.8 × 10−5 ± 0.9 × 10−5 RIU) at a cost of a narrow linear dynamic range (LDR, 1.3326–1.3548). In contrast, the single-microlens configuration led to an extended LDR (1.3326–1.5120 tested) despite the lower sensitivity (mean: 2.6 ± 0.2 AU·RIU−1) and resolution (mean: 1.5 × 10−4 ± 0.1 × 10−4 RIU). Furthermore, the use of the 3DCMOC was investigated via real-time salinity sensing and analysis of urine specific gravity.ISSN:1473-0197ISSN:1473-018

Optical-Switch-Enabled Microfluidics for Sensitive Multichannel Colorimetric Analysis

The implementation of colorimetric analysis within microfluidic environments engenders significant benefits with respect to reduced sample and reagent consumption, system miniaturization, and real-time measurement of flowing samples. That said, conventional approaches to colorimetric analysis within microfluidic channels are hampered by short optical pathlengths and single-channel configurations, which lead to poor detection sensitivities and low analytical throughputs. Although the use of multiplexed light source/photodetector modules allows for multichannel analysis, such configurations significantly increase both instrument complexity and cost. To address these issues, we present a four-channel colorimetric measurement scheme within an optical-switch-enabled microfluidic chip (OSEMC) fabricated by two-photon stereolithography. The integration of optical switches enables sequential signal readout from each detection channel, and thus, only a single light source and a photodetector are required for operation. Optical switches can be controlled in a bespoke manner by changing the medium in the switch channel between a “light-transmitting” fluid and a “light-blocking” fluid using pneumatic microvalves. Such optical switches are characterized by fast response times (approximately 200 ms), tunable switching frequencies (between 0.1 and 1.0 Hz studied), and excellent stability. Operational performance demonstrates both good sensitivity and reproducibility through the colorimetric analysis of nitrite and ammonium samples using four detection channels. Furthermore, the use of OSEMC for parallel and real-time analysis of flowing samples is investigated via characterization of the adsorption kinetics of tartrazine on activated charcoal and the catalytic reaction kinetics of horseradish peroxidase (HRP).ISSN:1520-6882ISSN:0003-270

Self-aligned 3D microlenses in a chip fabricated with two-photon stereolithography for highly sensitive absorbance measurement

Absorbance measurement is a widely used method to quantify the concentration of an analyte. The integration of absorbance analysis in microfluidic chips could significantly reduce the sample consumption and contribute to the system miniaturization. However, the sensitivity and limit of detection (LoD) of analysis in microfluidic chips with conventional configuration need improvements due to the limited optical pathway and unregulated light propagation. In this work, a 3D-microlens-incorporating microfluidic chip (3D-MIMC) with a greatly extended detection channel was innovatively fabricated using two-photon stereolithography. The fabrication was optimized with a proposed hierarchical modular printing strategy. Due to the incorporation of 3D microlenses, the light coupling efficiency and the signal-to-noise ratio (SNR) were respectively improved approximately 9 and 4 times. An equivalent optical path length (EOL) of 62.9 mm was achieved in a 3.7 μl detection channel for testing tartrazine samples. As a result, the sensitivity and LoD of the 3D-MIMC assay were correspondingly improved by one order of magnitude, compared with those of the 96-well plate assay. Notably, the 3D-MIMC has the potential to be integrated into a general microanalysis platform for multiple applications.ISSN:1473-0197ISSN:1473-018

Colorimetric immunodetection of bacteria enriched on membranes within a compact multichannel filtration device

Colorimetric immunoassay is a widely used method for pathogen detection. The conventional implementation of immunoassays in 96-well plates often encounters difficulties for samples with low concentrations. In this study, the detection performance has been improved using a cellulose acetate membrane for target enrichment and immunodetection. For this end, a compact multichannel filtration device was fabricated using a 3D printer for sample loading. Background effects of the membrane were greatly minimized after pretreatment with a sodium hydroxide solution to significantly reduce non-specific binding. The colorimetric result of the immunodetection of Escherichia coli strain K12 (E.coli K12) was recorded and quantitatively analyzed with a smartphone camera. A limit of detection was calculated as 40 cfu (colony forming unit)/ml, two orders of magnitude more sensitive than that obtained on 96-well plates with standard protocol. The developed approach features an integrated sample enrichment scheme, reduced reagents consumption, multiple channels for parallel processing and no reliance on advanced laboratory instruments, thereby providing potential for a low-cost and easy-to-use immunodetection system.ISSN:0925-400

An elution-based method for estimating efficiencies of aerosol collection devices not affected by their pressure drops

The evaluation of collection efficiencies of aerosol samplers becomes challenging with high pressure drops. The evaluation approaches applied at various conditions deserve further development, especially when a high pressure drop is induced by the sampler. In this work, an elution-based method using NaCl aerosol was proposed to estimate the size-resolved collection efficiency which was not affected by the pressure drop. More specifically, a Condensation Particle Counter (CPC) was used to count the upstream particle number, and the collected NaCl particles were eluted and determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for estimating the collected particle number. The relationship between number-based concentration and mass-based concentration of NaCl particles was established. A stainless steel impactor for Differential Mobility Analyzer (DMA), polydimethylsiloxane (PDMS)-based microchannel, and a homemade impactor containing 151 nozzles with a diameter of 0.1 mm were employed to investigate the feasibility of the elution method. DMA-selected particles with a nominal size are considered to be the monodisperse aerosol, which was commonly used for estimating the collection efficiencies of samplers, but size redistribution of downstream monodisperse aerosol with the particle size smaller than 100 nm and larger than the cutoff size (D50) was revealed through the elution method, which affected the collection efficiency measured by either conventional CPC- or elution-based method. It was found that the elution method was dependent on the D50 value of the sampler, and the applicable size range was from 100 nm to D50 (D50 < 500 nm) or from 100 nm to 500 nm (D50 greater than 500 nm). This study provided insights into the size-dependent particle transport through aerosol samplers, and the development of an elution-based method to estimate pressure drop-independent collection efficiencies.ISSN:1383-586

Thermoplasmonic-Assisted Cyclic Cleavage Amplification for Self-Validating Plasmonic Detection of SARS-CoV-2

The coronavirus disease 2019 (COVID-19) has penetrated every populated patch of the globe and sows destruction in our daily life. Reliable and sensitive virus sensing systems are therefore of vital importance for timely infection detection and transmission prevention. Here we present a thermoplasmonic-assisted dual-mode transducing (TP-DMT) concept, where an amplification-free-based direct viral RNA detection and an amplification-based cyclic fluorescence probe cleavage (CFPC) detection collaborated to provide a sensitive and self-validating plasmonic nanoplatform for quantifying trace amounts of SARS-CoV-2 within 30 min. In the CFPC detection, endonuclease IV recognized the synthetic abasic site and cleaved the fluorescent probes in the hybridized duplex. The nanoscale thermoplasmonic heating dehybridized the shortened fluorescent probes and facilitated the cyclical binding–cleavage–dissociation (BCD) process, which could deliver a highly sensitive amplification-based response. This TP-DMT approach was successfully validated by testing clinical COVID-19 patient samples, which indicated its potential applications in fast clinical infection screening and real-time environmental monitoring.ISSN:1936-0851ISSN:1936-086