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).

Total Bioaerosol Detection by a Succinimidyl-Ester-Functionalized Plasmonic Biosensor To Reveal Different Characteristics at Three Locations in Switzerland.

Bioaerosols consisting of biologically originated airborne particles such as microbes, metabolites, toxins, and fragments of microorganisms are present ubiquitously in our living environment. The international interests in bioaerosols have rapidly increased because of their many potential health effects. Thus, accurate and fast detection of total bioaerosols in different environments has become an important task for safeguarding against biological threats and broadening the pool of bioaerosol knowledge. To quickly evaluate the total bioaerosol concentration, we developed a localized surface plasmon resonance biosensor based on succinimidyl-ester-functionalized gold nanoislands (SEF-AuNIs) for quantitative bioaerosol detection. The detection limit of our proposed SEF-AuNI sensors for model bacteria Escherichia coli and Bacillus subtilis can go to 0.5119 and 1.69 cells/mL, respectively. To demonstrate the capability of this bioaerosol sensing technique, we tested aerosol samples collected from Bern (urban station), Basel (suburban station), and Rigi mountain (rural and high altitude station) in Switzerland and further investigated the correlation with endotoxin and PM10. The results substantiated that our SEF-AuNI sensors could be a reliable candidate for total bioaerosol detection and air quality assessment.

[Fingerprint Properties of Cephalosporin Pharmaceutical Wastewater].

Fluorescence spectrum is unique for each water sample, and is called "aqueous fingerprint". Aqueous fingerprint could indicate the contamination in water and thus is a new technology for early warning. Cephalosporin is one of the most commonly used antibiotics worldwide yet with environmental hazards. The production of cephalosporin in China is growing every year. Therefore, the study of aqueous fingerprint of cephalosporin pharmaceutical wastewater is significantly important for both monitoring the discharge of pharmaceutical wastewater and protecting the aquatic environment. In this study we investigated the properties of water fingerprint of cephalosporin pharmaceutical wastewater. There existed 6 peaks in the fingerprints. According to the emission wavelength, these peaks could be divided into two groups: the first group included the peaks locating at excitation wavelength/emission wavelength of 230/350, 275/350，315/350 nm and the second group consisted of the peaks locating at excitation wavelength/emission wavelength of 225/405, 275/410 and 330/420 nm respectively. The highest intensity was found at excitation wavelength/emission wavelength of 230/350 nm. In each group, the fluorescence intensity of the peaks with shorter excitation wavelength is higher. pH could significantly change the position and intensity of the peaks. When pH rose, the peak intensity of first group decreased and that of the second group increased. The intensity decrease is called fluorescence quenching and the intensity increase is called fluorescence sensitizing. The sensitizing and quenching was probably related to the fluorescence organic components with acid and alkaline radical groups in the wastewater. Because if a fluorescent substance contains weak acid or base groups, both the molecular configuration and ionic configurations exist in the solution at the same time. The spatial structure of these configurations are different. This makes the luminescent properties of the configurations different. When pH changes, the ratio of molecular configuration and ionic forms also changes, which causes the change of location and intensity of the fluorescence peaks. Above all, the properties of aqueous fingerprint of cephalosporin pharmaceutical wastewater is distinct and distinguishable. The properties of aqueous fingerprint can be used as a novel tool to identify the appearance of cephalosporin pharmaceutical wastewater.

[Pollution Source Identification of Water Body Based on Aqueous Fingerprint-Case Study].

Three-dimensional fluorescence spectroscopy is an emerging sensitive technology to detect organic pollution in water bodies. Based on this technique, a research group from Tsinghua University developed a novel instrument as a tool of pollution early-warning and pollution source identification，it has been put into use in A city in South China, for aqueous fingerprint monitoring and pollution sources identification under abnormal conditions. As a new monitoring method, it broke the limitation that traditional water quality monitoring technology could not provide directivity information of pollution source, and could detect abnormity of water quality quickly and identify pollution source accurately. In this paper, the process to identify pollution source during an abnormity incident of water quality in S River captured by the instrument was studied. When the instrument captured unidentified aqueous fingerprints during on-line monitoring, pollution intrusion process was inferred based on the variation of aqueous fingerprint figure and peak intensity. Then the pollution source identification was achieved by comparing the fingerprints between the polluted water body and possible pollution sources by the instrument. The source identification was verified with the changes of other water quality parameters such as pH, aniline, TOC and TN. The results showed that this early-warning and pollution source identification technique can quickly detect and release warning of abnormity of water quality and identify pollution sources accurately via monitoring aqueous fingerprints. The abnormity incident studied in this paper might be caused by dumping raw materials by a chemical plant located in upstream of the river.

[Fingerprint Properties of Semi Synthetic Penicillin Pharmaceutical Wastewater].

High-concentration antibiotics are detected in surface water from time to time. There has been an increasing demand for strengthening the supervision of the antibiotic pharmaceutical wastewater. Three-dimensional fluorescence technique is known as a rapid, simple and high-sensitivity method. The three-dimensional fluorescence spectrum can display organic components and it was named as aqueous fingerprint. In this paper, three-dimensional fluorescence characteristics of a typical semi synthetic penicillin pharmaceutical wastewater were studied. There were totally four fluorescence peaks in the aqueous fingerprint of this wastewater, locating in excitation wavelength/emission wavelength of 360/445, 255/445, 275/305 and 230/300 nm respectively. Fluorescence peak's intensity within certain range related linearly to the relative concentration. The possible fluorescent pollutants related to Peak C and Peak D might be the mixture of D-(-)-A-4-Hydroxyphenylglycine Dane Salt Methyl Potassium (pharmaceutical intermediates), Amoxicillin (pharmaceutical product) and D(-)-4-Hydroxyphenylglycine (pharmaceutical hydrolysate). PH played an important role in the fluorescence characteristics of this wastewater. This indicated that the fluorescent organic pollutants in this wastewater might contain acid or base groups. The aqueous fingerprint technique could be used to monitor the discharge of semi synthetic penicillin pharmaceutical wastewater as a novel tool.

Direct Quantitation of SARS-CoV-2 Virus in Urban Ambient Air via a Continuous-Flow Electrochemical Bioassay.

Airborne SARS-CoV-2 virus surveillance faces challenges in complicated biomarker enrichment, interferences from various non-specific matters and extremely low viral load in the urban ambient air, leading to difficulties in detecting SARS-CoV-2 bioaerosols. This work reports a highly specific bioanalysis platform, with an exceptionally low limit-of-detection (≤1 copy m-3 ) and good analytical accordance with RT-qPCR, relying on surface-mediated electrochemical signaling and enzyme-assisted signal amplification, enabling gene and signal amplification for accurate identification and quantitation of low doses human coronavirus 229E (HCoV-229E) and SARS-CoV-2 viruses in urban ambient air. This work provides a laboratory test using cultivated coronavirus to simulate the airborne spread of SARS-CoV-2, and validate that the platform could reliably detect airborne coronavirus and reveal the transmission characteristics. This bioassay conducts the quantitation of real-world HCoV-229E and SARS-CoV-2 in airborne particulate matters collected from road-side and residential areas in Bern and Zurich (Switzerland) and Wuhan (China), with resultant concentrations verified by RT-qPCR.

Microfluid Switching-Induced Transient Refractive Interface.

The laminar flow interface (LFI) developed at low Reynolds numbers is one of the most prominent features of microscale flows and has been employed in a diverse range of optofluidic applications. The formation of LFIs usually requires the manipulation of multiple streams within a microchannel using a complex hydrodynamic pumping system. Herein, we present a new type of LFI that is generated by fluid switching within a three-dimensional (3D) microlens-incorporating microfluidic chip (3D-MIMC). Since Poiseuille flows exhibit a parabolic velocity profile, the LFI is cone-like in shape and acts as a transient refractive interface (TRI), which is sensitive to the refractive index (RI) and the Péclet number (Pe) of the switching fluids. In response to the TRI, the intensity of the transmitted light can be intensified or attenuated depending on the sequence of fluid switching operations. By incorporating three-dimensional (3D) microlenses and increasing the Pe values, the profile and amplitude of the intensity peak are both significantly improved. The limit of detection (LoD) for a sodium chloride (NaCl) solution at Pe = 1363 is as low as 0.001% (w/w), representing an improvement of 1-2 orders of magnitude when compared to existing optofluidic concentration sensors based on intensity modulation. Fluid switching of a variety of inorganic and organic sample fluids confirms that the specific optical response (Kor) correlates positively with both Pe and the specific RI (Knc), obeying a linear relationship. This model is further verified through cross-validations and used to estimate the molecular diffusion coefficient (D) of a range of species. Furthermore, by virtue of the TRI, we achieve a sensitive measurement of optical-equivalent total dissolved solids (OE-TDS) for environmental samples.

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.

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.

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.

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.

Identification of textile wastewater in water bodies by fluorescence excitation emission matrix-parallel factor analysis and high-performance size exclusion chromatography.

Identifying the causes of water body pollution is critical because of the serious water contamination in developing countries. The textile industry is a major contributor to severe water pollution due to its high discharge of wastewater with high concentrations of organic and inorganic pollutants. In this study, fluorescence excitation emission matrix-parallel factor (EEM-PARAFAC) analysis was applied to characterize textile industry wastewater and trace its presence in water bodies. The EEM spectra of textile wastewater samples collected from 12 wastewater treatment plants (WWTPs) revealed two characteristic peaks: Peak T1 (tryptophan-like region) and Peak B (tyrosine-like region). Two protein-like components (C1 and C2) were identified in the textile wastewater by PARAFAC analysis. The components identified from different textile WWTPs were considered identical (similarity >0.95). C1 and C2 were not sensitive to changes in pH, ionic strength, or low humic acid concentration (TOC < 4 mg/L). Therefore, C1 combined with C2 was proposed as a source-specific indicator of textile wastewater, which was further demonstrated by conducting high-performance size exclusion chromatography analysis. These results suggested that EEM-PARAFAC analysis is a reliable means of identifying textile wastewater pollution in water bodies and may also enable the identification of other industrial wastewater.

Novel insights into variation of fluorescent dissolved organic matters during antibiotic wastewater treatment by excitation emission matrix coupled with parallel factor analysis and cosine similarity assessment.

In this work, the variation of fluorescent dissolved organic matters (FDOM) of antibiotic wastewater in a full-scale treatment plant was studied. Fluorescent components of anaerobic, aerobic, Fenton stages were separately figured out by parallel factor analysis (PARAFAC) based on excitation emission matrix (EEM) dataset. Then, these components were pairwise quantitatively compared according to cosine similarity (CS). It was found that, after the anaerobic treatment, the major components showed remarkable similarity (CS > 0.97) to those of raw wastewater, although their maximum fluorescence intensity (Fmax) decreased slightly or moderately (7% ∼ 54%). However, the aerobic treatment dramatically changed both the composition and content of fluorescent components, as all the protein-like components completely disappeared and only the humic-like components with much lower intensity were observed. After Fenton oxidation, all these humic-like components were remained (CS > 0.97) with fairly reduced Fmax (51% ∼ 61%). For both aerobically treated and Fenton-oxidized wastewater, Fmax correlated well with dissolved organic carbon (DOC). This suggested a dominant proportion of humic-like substances. The combination of PARAFAC based on separate EEM dataset of each treatment stage and CS assessment is a good approach to better understand FDOM variation and can be of much practical significance to monitor wastewater quality.