Extraction of C-reactive protein from serum on a microfluidic chip

Heterologous expression of human C-reactive protein in the green alga Chlamydomonas reinhardtii

C-reactive protein (CRP) participates in human inflammatory responses and is an important indicator in clinical diagnoses. At present, the use of monoclonal antibodies to detect CRP in the human body is high, but they are unstable and expensive. Understanding the CRP expression pathway is of great significance for developing CRP tests and reagents. Chlamydomonas reinhardtii is a model organism that has great potential as a foreign protein expression system. This study is the first attempt to express human CRP in C. reinhardtii. We selected the endogenous constitutive Rbcs2 promoter and terminator and used ble as a selective gene to construct a C. reinhardtii nuclear expression vector containing CRP. After transformation using the glass bead method, six positive transformants were obtained. At the molecular level, full-length CRP was transformed into the genome of C. reinhardtii CC400 cells, and human CRP was expressed. This study provides new insights into obtaining active CRP. PRACTICAL APPLICATIONS: Based on the nuclear transformation system of C. reinhardtii, it can construct an exogenous protein expression system that produces a variety of high value-added products and can be used to produce a variety of high value-added proteins, functional drugs, and industrial raw materials. It has broad market prospects and huge application prospects.

Miniaturization of the Whole Process of Protein Crystallographic Analysis by a Microfluidic Droplet Robot: From Nanoliter-Scale Purified Proteins to Diffraction-Quality Crystals

To obtain diffraction-quality crystals is one of the largest barriers to analyze the protein structure using X-ray crystallography. Here we describe a microfluidic droplet robot that enables successful miniaturization of the whole process of crystallization experiments including large-scale initial crystallization screening, crystallization optimization, and crystal harvesting. The combination of the state-of-the-art droplet-based microfluidic technique with the microbatch crystallization mode dramatically reduces the volumes of droplet crystallization reactors to tens nanoliter range, allowing large-scale initial screening of 1536 crystallization conditions and multifactor crystallization condition optimization with extremely low protein consumption, and on-chip harvesting of diffraction-quality crystals directly from the droplet reactors. We applied the droplet robot in miniaturized crystallization experiments of seven soluble proteins and two membrane proteins, and on-chip crystal harvesting of six proteins. The X-ray diffraction data sets of these crystals were collected using synchrotron radiation for analyzing the structures with similar diffraction qualities as conventional crystallization methods.

Biomimetic Polymer-Based Method for Selective Capture of C-Reactive Protein in Biological Fluids

Selective capturing and purification of C-reactive protein (CRP) from complex biological fluids plays a pivotal role in studying biological activities of CRP in various diseases. However, obvious nonspecific adsorption of proteins was observed on current affinity sorbents, and thus additional purification steps are often required, which could compromise the recovery of the target protein and/or introduce new impurities. In this study, inspired by the highly specific interaction between CRP and the cell membrane, an excellent anti-biofouling compound 2-(methacryloyloxy)ethyl phosphorylcholine and a highly hydrophilic crosslinker N, N'-methylenebisacrylamide were employed to fabricate a novel cell membrane biomimetic polymer for selective capture of CRP in the presence of calcium ions. Based on the polymer described above, a facile enrichment approach was established after systematic optimization of the washing and elution conditions. With its favorable properties, such as good porosity, weak electrostatic interaction, high hydrophilicity, and biocompatibility, the novel biomimetic polymer exhibits good specificity, selectivity, recovery (near 100%), purity (95%), and a lower nonspecific protein adsorption for CRP in comparison with commercial immobilized p-aminophenyl phosphoryl choline gel and other purification materials. Furthermore, the structural integrity and functionality of CRP in the elution fraction were well preserved and confirmed by circular dichroism spectroscopy, fluorescence spectroscopy, and immunoturbidimetric assay. Finally, the biomimetic polymer was successfully applied to the selective enrichment of CRP from sera of patients with inflammation and rats. The proposed novel enrichment approach based on the versatile biomimetic polymer can be used for effective CRP purification, which will benefit the in-depth study of its biological roles.

Homogeneous capture and heterogeneous separation of proteins by PEG-functionalized ionic liquid–water systems

An efficient homogeneous capture and heterogeneous separation strategy for proteins is reported using PEG-functionalized ionic liquids with LCST phase behavior in water.

A Porous Microfluidic Chip for Protein Extraction Based on Solid Phase Extraction Method

Based on the principle of solid phase extraction (SPE) and the special immunoreaction, a microfluidic chip integrated with porous matrix was developed for protein extraction. Porous matrix was achieved by electrochemical etching silicon in a HF/ethanol mixture, which was coated on the wall of the rectangular channel of the microchip to provide a surface-enlarging matrix. The surface morphology of the bare porous silicon and the porous silicon modified with the protein has been characterized by SEM. Non-porous chip and porous chip were used to extract protein. Compared with non-porous matrix, the porous matrix achieved higher extracted efficiency of protein. Then two methods of surface modification were employed on porous matrix for protein extraction. The surface modification with Protein A could extract more protein with less non-special absorption. Evaluation of the structure of the solid phase matrix and the surface modification process in the microfluidic chip, the porous microfluidic chip is able to be suitable for incorporation into micro total analysis system (μTAS).

A continuous-flow, microfluidic fraction collection device

A microfluidic device is presented that performs electrophoretic separation coupled with fraction collection. Effluent from the 3.5 cm separation channel was focused via two sheath flow channels into one of seven collection channels. By holding the collection channels at ground potential and varying the voltage ratio at the two sheath flow channels, the separation effluent was directed to either specific collection channels, or could be swept past all channels in a defined time period. As the sum of the voltages applied to the two sheath flow channels was constant, the electric field remained at 275 V/cm during the separation regardless of the collection channel used. The constant potential in the separation channel allowed uninterrupted separation for late-migrating peaks while early-migrating peaks were being collected. To minimize the potential for carryover between fractions, the device geometry was optimized using a three-level factorial model. The optimum conditions were a 22.5° angle between the sheath flow channels and the separation channel, and a 350 μm length of channel between the separation outlet and the fraction channels. Using these optimized dimensions, the device performance was evaluated by separation and fraction collection of a fluorescently-labeled amino acid mixture. The ability to fraction collect on a microfluidic platform will be especially useful during automated or continuous operation of these devices or to collect precious samples.

Aptamer-antibody on-chip sandwich immunoassay for detection of CRP in spiked serum

This study describes a RNA aptamer-based biochip with high affinity and specificity for C-reactive protein (CRP). CRP, which exists in concentrations of 1-3mg/l in the serum of healthy patients, has been identified as a reliable biomarker for inflammation and as a potential marker for sepsis and tissue necrosis. The CRP-specific aptamer was covalently immobilized with its 5'-end on ARChip Epoxy. The detection of bound CRP was carried out optically using labelled secondary antibody in a sandwich format. Assay conditions were optimized with respect to the CRP binding buffer (buffer system, pH and additives) and Ca(2+) concentration (10 mM). Moreover, two sandwich immunoassay formats were tested, the one using dye-labelled antibodies and the other with biotin-modified antibodies/Dy647-labelled streptavidin. In comparison with an antibody-based chip assay, the aptamer chip is superior in terms of CRP measuring range (10 microg/l to 100mg/l) in human serum whereas antibody-based chips result in superior data reproducibility (CV of 8-15%). In contrast to antibody chips, aptamer microarrays provide the unique potential of detecting CRP in serum samples of low risk patients (1-3mg/l) as well as high risk patients (>500 mg/l), furthermore elevated CRP levels (20-350 mg/l) with acceptable recovery (70-130%) by including only one serum sample dilution step (1:100) for the complete measuring range.

Towards an integrated microfluidic device for spaceflight clinical diagnostics Microchip-based solid-phase extraction of hydroxyl radical markers

A microchip-based solid-phase extraction method for biological fluid small molecule analysis has been developed. Using a commercially available copolymer packed into a microchip channel, extraction and preconcentration of 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA from saliva was achieved. The metabolites, formed from salicylic acid by reactive oxygen species, can be used as markers of oxidative stress. The results show high recovery of both metabolites (>90+/-15% for spiked saliva) with an 80-fold concentration enhancement possible. The eluent is directly analyzed using capillary electrophoresis, with good resolution for the two metabolites. This study demonstrates the feasibility of future integrated microdevices for spaceflight small molecule biomarker analysis.

Microfluidic capillary system for immunoaffinity separations of C-reactive protein in human serum and cerebrospinal fluid

A miniaturized system based on microfluidic capillaries is presented for point-of-care testing and clinical assessment. The approach relies on microsyringe pump-generated flow to deliver reagents and immunoaffinity chromatography to isolate the antigen from biological matrixes. Capillary sandwich immunoassays for C-reactive protein (CRP) were demonstrated in human serum and cerebrospinal fluid (CSF), which are relevant matrixes for cardiovascular disease risk and meningitis research, respectively. Capillaries packed with antibody-coated silica beads were used to capture CRP from the matrix and a second, dye-labeled antibody was introduced to form a sandwich complex. An acidic elution buffer dissociated the antibody-antigen complexes, and the labeled antibody was detected with diode laser-induced fluorescence. Four parameter logistic functions and % relative error plots were used to model and assess the data. The calibration ranges for CRP were 0.05-3.0 microg/mL in 1:10 diluted serum and 0.01-30 microg/mL in undiluted CSF. The microfluidic apparatus employed a flow rate of 2 microL/min and a sample injection volume of 250 nL. Since it was not necessary to reach antibody-antigen reaction equilibrium and the assay platform dimensions were minimal, run times were as short as 10 min.

Infrared Temperature Control System for a Completely Noncontact Polymerase Chain Reaction in Microfluidic Chips

A completely noncontact temperature system is described for amplification of DNA via the polymerase chain reaction (PCR) in glass microfluidic chips. An infrared (IR)-sensitive pyrometer was calibrated against a thermocouple inserted into a 550-nL PCR chamber and used to monitor the temperature of the glass surface above the PCR chamber during heating and cooling induced by a tungsten lamp and convective air source, respectively. A time lag of less than 1 s was observed between maximum heating rates of the solution and surface, indicating that thermal equilibrium was attained rapidly. Moreover, the time lag was corroborated using a one-dimensional heat-transfer model, which provided insight into the characteristics of the device and environment that caused the time lag. This knowledge will, in turn, allow for future tailoring of the devices to specific applications. To alleviate the need for calibrating the pyrometer with a thermocouple, the on-chip calibration of pyrometer was accomplished by sensing the boiling of two solutions, water and an azeotrope, and comparing the pyrometer output voltage against the known boiling points of these solutions. The "boiling point calibration" was successful as indicated by the subsequent chip-based IR-PCR amplification of a 211-bp fragment of the B. anthracis genome in a chamber reduced beyond the dimensions of a thermocouple. To improve the heating rates, a parabolic gold mirror was positioned above the microfluidic chip, which expedited PCR amplification to 18.8 min for a 30-cycle, three-temperature protocol.