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The surface modification technique is applied in microfluidic devices to modify wettability and achieve different flow velocities. Currently available methods for poly(dimethylsiloxane) (PDMS) surfaces may reliably induce wettability changes, but only one area can be altered at a time. This work introduces the controlled gradient oxygen plasma modification (CGPM) technique, which layers several resin masks with varying porosities on top of the PDMS surface. Selective wettability of the PDMS surface can be achieved by varying the oxygen plasma density above the modified material's surface by manipulation of the porosity value. Through the implementation of the COMSOL plasma module, the impact of the mask's porosity, through-hole size, distribution, and distance from the PDMS surface on wettability was studied. The suggested CGPM approach was characterized by contact angle measurements. During the 25-second CGPM procedure, the PDMS surface's contact angle continually changed from 8.77° to 76.98°. An integrated microfluidic device was created and manufactured to identify D-dimers to illustrate this method. In comparison with standard oxygen plasma treatment, the D-dimer assay was finished in 10 minutes and had a dynamic range of 1–1000 ng mL−1, with a peak fluorescence signal augmentation of 78.3% and an average fluorescence intensity enhancement of 31.1%. [ABSTRACT FROM AUTHOR]

Breath analysis may provide a convenient and non-invasive method for clinical monitoring of chronic kidney disease (CKD) progression. However, few breath volatile organic compounds (VOCs) indicating progression of CKD have been reported. In this study, we used gas chromatography-mass spectrometry (GC-MS) for untargeted detection of breath VOCs in stage 1, 3, and 5 CKD patients. The results showed that, the levels of breath 4-heptanone, n-octane, and n-dodecane gradually increased from CKD stage 1 to stage 5, and their increasing rates from CKD stage 3 to stage 5 were higher than those from CKD stage 1 to stage 3. Gender, smoking habits, age, and body mass index (BMI) had insignificant impact on the levels of the three breath VOCs. The accuracies of the polynomial support vector machine (SVM) and K-nearest neighbour (KNN) models based on 4-heptanone + n-octane + n-dodecane combination in distinguishing CKD stages 1, 3, and 5 were 76.3% and 72.8%, respectively. The combination of 4-heptanone + n-octane + n-dodecane was superior to any single component for monitoring CKD progression. These discoveries have valuable implications for long-term clinical monitoring of CKD and improving our understanding of CKD. [ABSTRACT FROM AUTHOR]

The trace-level detection of harmful NO2 gas at room-temperature is very important for environmental protection and public health. This paper reports the resonant-gravimetric detection of ppb-level NO2 at room-temperature using two-dimensional porous TiO2 nanosheets (PTNSs) as highly active sensing materials. They are synthesized by a facile high-temperature calcination approach based on a graphene oxide self-sacrificial template. The PTNS sample prepared at 500 °C (TiO2-500 °C) show an anatase structure, while the sample prepared at 800 °C (TiO2-800 °C) contains an impurity rutile phase. By loading pure anatase PTNSs onto resonant microcantilevers, the sensors exhibit high sensitivity to NO2 gas with a limit of detection as low as 15 ppb. Compared with the TiO2-800 °C sample, the much higher sensitivity of the TiO2-500 °C sample can be attributed to the bigger adsorption enthalpy (–ΔH°) of pure anatase TiO2 to NO2 gas molecules (21.7 and 57.8 kJ mol−1, respectively). Density functional theory calculations further demonstrate that the existence of the rutile impurity phase in the TiO2-800 °C sample results in its significantly decreased adsorption activity to NO2. This work approves the great application potential of anatase PTNSs for the highly sensitive resonant-gravimetric detection of NO2 gas at room-temperature. [ABSTRACT FROM AUTHOR]

The detection of organophosphorus (OP) compounds, which are extremely toxic, is a requirement in many application fields such as food security. Mass-type chemical sensors based on ultra-sensitive resonant microcantilevers exhibit high comparative advantages in OP compound detection. However, it is still a big challenge to construct a sensing film in situ from corrosive precursors on resonant cantilevers for batch fabrication. In this work, Parylene-C is patterned and a sample reservoir is formed on the free-end of resonant microcantilever for constructing the sensing material directly. Not only utilized for corrosive precursor loading and in situ sensing material construction, the Parylene-C film can also be used to effectively protect the integrated elements from damage by corrosive substances. For extremely toxic OP molecule detection, a typical metal–organic framework (MOF) of UiO-66 film has been regioselectively constructed in situ on the Parylene-C patterned microcantilevers. A limit of detection (LOD) of 5 ppb for the OP simulant dimethyl methylphosphonate (DMMP) is achieved. The in situ MOF construction method manifests satisfactory consistency for sensor batch fabrication. The DMMP sensing mechanism is identified as the specific host–guest interaction between the UiO-66 and OP molecule. [ABSTRACT FROM AUTHOR]

Members of the Brucella spp. are facultative intracellular bacteria that can cause global brucellosis, a zoonotic disease. Herein, a novel fluorescence signal amplification (FSA) method for the rapid detection of B. melitensis 16M was developed based on peptide-mediated magnetic separation (PMS) technology and Au nanoparticle (AuNP)-mediated bio-barcode assay technology assembled by quantum dots (QDs). The PMS technology was used to specifically capture and isolate B. melitensis 16M from food. The immunomagnetic bead-B. melitensis 16M bioconjugates (IMBs-B. melitensis 16M) were then identified by IgY on the surface of AuNPs and the oligonucleotide chains on the surface of the gold nanoparticles were hybridized with bio-barcodes assembled by quantum dots (QD-probe2). The IMB/B. melitensis 16M/IgY–AuNP-probe1/QD-probe2 bioconjugates were concentrated by magnetic separation. Therefore, as the concentration of B. melitensis 16M in the sample increased, the unbound QD-probe2 in the supernatant reduced, and the B. melitensis 16M in the sample could be indirectly measured by detecting the fluorescence in the supernatant. This FSA method can detect B. melitensis 16M concentration in the range of 10 to 106 cfu ml−1 without pre-enrichment, and the limit of detection (LOD) is as low as 10 cfu ml−1 with high specificity. Furthermore, the proposed method for the detection of B. melitensis 16M has a LOD of 1.07 × 102 cfu ml−1 and a linear range from 102 to 107 cfu ml−1 in milk, and a LOD of 1.72 × 102 cfu ml−1, and a linear range from 102 to 106 cfu ml−1 in lamb leach. In addition, this method takes less than 3 h to perform. Thus, the assay that was developed in this study shows promise for rapid, sensitive, and specific detection of B. melitensis 16M. [ABSTRACT FROM AUTHOR]

The trace-level detection of harmful NO2 gas at room-temperature is very important for environmental protection and public health. This paper reports the resonant-gravimetric detection of ppb-level NO2 at room-temperature using two-dimensional porous TiO2 nanosheets (PTNSs) as highly active sensing materials. They are synthesized by a facile high-temperature calcination approach based on a graphene oxide self-sacrificial template. The PTNS sample prepared at 500 °C (TiO2-500 °C) show an anatase structure, while the sample prepared at 800 °C (TiO2-800 °C) contains an impurity rutile phase. By loading pure anatase PTNSs onto resonant microcantilevers, the sensors exhibit high sensitivity to NO2 gas with a limit of detection as low as 15 ppb. Compared with the TiO2-800 °C sample, the much higher sensitivity of the TiO2-500 °C sample can be attributed to the bigger adsorption enthalpy (-ΔH°) of pure anatase TiO2 to NO2 gas molecules (21.7 and 57.8 kJ mol-1, respectively). Density functional theory calculations further demonstrate that the existence of the rutile impurity phase in the TiO2-800 °C sample results in its significantly decreased adsorption activity to NO2. This work approves the great application potential of anatase PTNSs for the highly sensitive resonant-gravimetric detection of NO2 gas at room-temperature.

This research investigates the origin of specific molecule-adsorption induced surface-stress for micro/nano-cantilever bio/chemical sensors. Systematic discussion is presented on the contribution from types of molecule interactions to the generated surface-stress sensing signal. With the main arguments verified by our micro-cantilever sensing experiments, the origin of the adsorption induced surface-stress is, for the first time, clearly categorized into interface vertical effects and lateral interactions, which helps to comprehensively understand the surface-stress generation and overall to optimize the sensing performance of micro-cantilever chemo-mechanical sensors. The key findings of this research are that, vertically at the molecule adsorption surface, interfacial energy change and charge redistribution are the main origins of the generated surface-stress. More importantly, intermolecular lateral interactions may make a more significant contribution to the nano-mechanical surface-stress response. Compared with other lateral interactions like van der Waals force and the electrostatic coulombic effect, intermolecular hydrogen-bond intensity and steric factor easily cause much greater disparity in surface-stress.