The COVID-19 pandemic caused by SARS-CoV-2 is a health threat worldwide. Viral main protease (Mpro, also called 3C-like protease, 3CLpro) is a therapeutic target for drug discovery. Herein, we report that GC376, a broad-spectrum inhibitor targeting Mpro in the picornavirus-like supercluster, is potent inhibitor for the Mpro encoded by SARS-CoV-2 with half-maximum inhibitory concentration (IC50) of 26.4±1.1 nM. In this study, we also show that GC376 inhibits SARS-CoV-2 replication with a half-maximum effective concentration (EC50) of 0.91±0.03 μM. Only a small portion of SARS-CoV-2-Mpro was covalently modified in the excess of GC376 as evaluated by mass spectrometry analysis; indicating that improved inhibitors are needed. Subsequently, molecular docking analysis revealing the recognition and binding groups of GC376 within the active site of SARS-CoV-2 Mpro provides important new information for the optimization of GC376. Given that sufficient safety and efficacy data are available for GC376 as an investigational veterinary drug, expedited development of GC376, or its optimized analogues, for treatment of SARS-CoV-2 infection in human is recommended.

Poly(dimethylsiloxane) (PDMS) is a biomaterial that presents serious surface instability characterized by hydrophobicity recovery. Permanently hydrophilic PDMS surfaces were created using electrostatic self-assembly of polyethyleneimine and poly(acrylic acid) on top of a hydrolyzed poly(styrene-alt-maleic anhydride) base layer adsorbed on PDMS. Cross-linking of the polyelectrolyte multilayers (PEMS) by carbodiimide coupling and covalent attachment of poly(ethylene glycol) (PEG) chains to the PEMS produced stable, hydrophilic, protein-resistant coatings, which resisted hydrophobicity recovery in air. Attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the thin films had excellent chemical stability and resisted hydrophobicity recovery in air over 77 days of measurement. The spectra also showed a dense coverage for PEG dialdehyde and excellent resistance to protein adsorption from undiluted rat serum. Atomic force microscopy revealed dense coverage with PEG dialdehyde and PEG diamine. Contact angle measurements showed that all films were hydrophilic and that the PEG dialdehyde-topped thin film had a virtually constant contact angle (approximately 20 degrees ) over the five months of the study. Electrokinetic analysis of the coatings in microchannels always exposed to air also gave good protein separation and constant electroosmotic flow during the five months that the measurements were done. We expect that the stable, hydrophilic, protein-resistant thin-film coatings will be useful for many applications that require long-term surface stability.

We present the current status of the development of microfluidic devices fabricated on different substrates for coupling with electrospray ionization-mass spectrometry (ESI-MS). Until now, much success has been gained in fabricating the ESI chips, which show better performances due to miniaturization when compared with traditional methods. Integration of multiple steps for sample preparation and ESI sample introduction, however, remains a great challenge. This review covers the main technical development of electrospray device that were published from 1997 to 2004. This article does not attempt to be exclusive. Instead, it focuses on the publications that illustrated the breath of the development and applications of microchip devices for MS-based analysis.

This study presents an active method for micro-mixers using surface acoustic waves (SAW) to rapidly mix co-fluent fluids. Mixing is challenging work in microfluidic systems due to their low-Reynolds-number flow conditions. SAW devices were fabricated on 128 • Y-cut lithium niobate (LiNbO 3 ). The micro-mixers are these piezoelectric actuators integrated with polydimethylsiloxane microchannels. The effects of the applied voltages on interdigitated transducers (IDTs) and two layouts, parallel-and transversal-type, of micro-mixers on the mixing performance were experimentally explored. The experimental results revealed that the parallel-type mixer achieved a higher mixing effect. Meanwhile, a higher applied voltage on the IDTs led to a significant improvement in the mixing performance of the active micro-mixer. Typical temperature effects associated with the applied voltages on the IDTs were also investigated. Finally, a digestion reaction between a protein (hemoglobin) and an enzyme (trypsin) was performed to verify the capability of the micro-mixers. The protein-enzyme mixture was qualitatively analyzed using mass spectrometry. Using these SAW-based mixers, the amount of digested peptides increased. Additionally, the protein-enzyme mixture was also quantitatively analyzed using high-performance liquid chromatography. Experimental data showed that the amount of digested peptides increased 21.1% using the active mixer. Therefore, the developed micro-mixers can be applied in microfluidic systems for improving mixing efficiency and thus enhancing the bio-reaction.

Poly(dimethylsiloxane) (PDMS) possesses many advantages, such as biocompatibility and high oxygen permeability, which makes it an attractive material for fabricating biodevices. Creating an affinity surface with long-term stability and reactivity for biomolecular interactions on a PDMS substrate, however, is difficult due to its inherent hydrophobicity. In this study, an affinity surface on a PDMS substrate with long-term hydrophilicity and affinity reactivity is reported. This modification is composed of two parts. The bottom part is made of polyelectrolyte multilayers and is capable of providing long-term hydrophilic stability. The top part consists of three protein layers, bovine serum albumin (BSA), anti-BSA, and protein G, and offers an affinity surface for antibody binding and, more importantly, provides favorable orientation and minimum nonspecific binding. The chemical modification for the different stages was monitored by atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR), and contact angle and fluorescence measurements. A long-term PDMS immunodevice (LPID) based on polyelectrolyte multilayers and protein layers was fabricated and applied to the detection of transforming growth factor beta (TGF-beta) protein in mouse serum by the enzyme-linked immunosorbent assay (ELISA) method. Results show that a linear calibration curve was obtained in the concentration range from 500 to 15.125 pg/mL, and the relative standard deviation was less than 3%. Also, the amount of TGF-beta spiked in mouse serum was precisely determined. Results indicate that the modified surface was hydrophilic and reactive to biospecies up to more than 7 days in its dry form. Moreover, the blocking reagent used to reduce nonspecific binding was found to be not necessary for the LPID. Thus, the reported method is expected to hold a great potential for fabricating PDMS-based affinity devices such as protein chips.

An easy method to fabricate poly(dimethylsiloxane) (PDMS)-based microfluidic chips for protein identification by tandem mass spectrometry is presented. This microchip has typical electrophoretic microchannels, a flow-through sampling inlet, and a sheathless nanoelectrospray ionization (ESI) interface. The surface of the microchannel was modified with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and the generated electroosmotic flow under acidic buffer condition used for the separation was found to be more stable compared to that generated by the microchannel without modification. The feasibility of the device for flow-through sampling, separation, and ESI-MS/MS analysis was demonstrated by the analysis of a standard mixture composed of three tryptic peptides. Results show that four peaks corresponding to three peptide standards and acetylated products of the standard peptide were well resolved and the deduced sequences were consistent with those expected. Furthermore, the compatibility of this device with other miniaturized devices to integrate the whole process was also explored by connecting a miniaturized enzymatic digestion cartridge and a desalting cartridge in series to the sampling inlet of the microchip for the identification of a model protein, beta-casein.

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Integration of a hydrogel and polydimethylsiloxane (PDMS)-based microfluidic device can greatly reduce the cost of developing channel-based devices. However, there are technical difficulties including the hydrophobic and inert surface properties associated with PDMS as well as back pressure and fragile material associated with the use of hydrogel in microchannels. In this study, a strategy to covalently photopattern 3-D hydrogel plugs with functionalized protein G inside microfluidic channels on a hydrophilic PDMS substrate coated with polyelectrolyte multilayers (PEMS) is presented. In this process, a UV-light microscope is applied to initiate the protein G-poly(acryl amide) copolymerization from the bulk substrate to solution areas via the deeply implanted photoinitiator (PI), resulting in sturdy 3D plugs covalently bonded to the upper and lower channel wall, while leaving open spaces in the channel width for the fluid to flow through. In addition, the long-term hydrophilicity and low nonspecific binding property associated with PEMS surface can be conserved for the nonpatterned area, leading to hydrogel plugs in extremely hydrophilic and permeable environment in a restricted channel space for bubble-free fluid transport and affinity interaction. By immobilization of well-oriented antibodies via protein G on the hydrogel plugs in the channel, estrogen receptor alpha (ERalpha) is demonstrated to be captured quantitatively with high loading capacity and high specificity.