SI-traceable calibration-free analysis for the active concentration of G2-EPSPS protein using surface plasmon resonance

Quantification of Cry1Ab protein in genetically modified plants based on immunoaffinity magnetic bead enrichment and high-performance liquid chromatography-tandem mass spectrometry

Quantification of Cry1Ab in genetically modified (GM) plants based on immunoaffinity magnetic bead enrichment and high-performance liquid chromatography-tandem mass spectrometry was developed. The active concentration of Cry1Ab standard solution was determined via surface plasmon resonance. Magnetic beads coated with Cry1Ab monoclonal antibodies were used for affinity enrichment of the target protein from samples. After trypsin digestion, quantification was performed by LC-MS/MS with internal standards, showing the recovery rate of (93.2 %-110.69 %) and relative standard deviation of (2.4 %-4.8 %, n = 12). The limit of detection was 5.7 ng/mL, and the limit of quantification was 22.5 ng/mL. The method was further validated by comparing the measured Cry1Ab concentrations in GM soybean and corn leaves with those obtained using ELISA. This method enables facilitating accurate quantitation of Cry1Ab and the assessment of environmental impact, pest control efficacy, and safety of GM crops.

Absolute quantification of Neuron-specific enolase based on surface plasmon resonance

Neuron-specific enolase (NSE) is currently the most reliable biomarker for small cell lung cancer (SCLC), which is important for disease monitoring, clinical evaluation and diagnosis. However, traditional methods suffer from various disadvantages, including instability, complexity, time-consuming operations, and the necessity for standards. In this study, we developed a calibration-free concentration analysis (CFCA) method based on surface plasmon resonance (SPR) technology, to accurately quantify the active concentration of NSE without relying on any standards. Based on the principle of CFCA, the active concentration of NSE can be calculated by observing binding rate variations at two flow rates under partial mass transport limitation and combining it with the known diffusion coefficient of the NSE. Using the method of CFCA, the active concentration of NSE was determined was only 0.48 mg/mL with an intra-day repeatability of 4.75%. The method has the advantages of simplicity, rapidity, realistic analysis and ease of implementation of high-throughput automated detection. Therefore, the method is expected to become the main measurement method for protein active concentration, which will be beneficial for the development of active protein standards.

Absolute quantification of microRNAs based on mass transport limitation under a laminar flow SPR system

As an important biomarker for diagnostics and therapeutics of various diseases, the low-cost, quantitative detection method of microRNAs (miRNAs) has recently caught broad attention. However, their small size and low abundance still derive challenges to quantification detection. In this study, we developed an ultrasensitive and multiplexed surface plasmon resonance (SPR) biosensor for quantifying miRNAs without standard. We introduced the mass transport limitation (MTL) strategy for the absolute quantification of miRNAs. We first explore the mechanism of DNA capture and the condition for triggering MTL on the SPR biosensor. We demonstrated that probes of 22-25 nt in length with fewer influences of the secondary structure provide better triggering of MTL. For proof of concept studies, let-7a, miR-155 and miR-21 were selected as candidate targets. Based on the structure and kinetics analysis, we demonstrate the best capture probe efficiency, and this biosensor's limit of detection (LOD) is 500 fM without any signal amplification. Furthermore, our biosensor achieves multiplex detection, which could detect three targets simultaneously. The quantitative results of miRNA indicated the great prospects of our biosensor in nucleic acid-related early diagnosis and biosensing.

A multiplex and regenerable surface plasmon resonance (MR-SPR) biosensor for DNA detection of genetically modified organisms

The continuous advancement of analytical technology has provided methods with increasing sensitivity and precision to detect genetically modified organisms (GMOs). Novel analytical strategy-based detection methods are alternatives to conventional polymerase chain reaction (PCR)-mediated assays, which are still the gold standard in this field. However, PCR primers and probes cannot be reused, which makes the technique uneconomical. Surface plasmon resonance (SPR) is an optical and label-free technique for studying ligand-analyte interactions, especially for DNA hybridization, and several SPR biosensors have been described for the detection of nucleic acids. Here, a multiplexed, regenerable and real-time SPR biosensor for the detection of GMOs is described. A biosensor was constructed for qualitative detection of T-nos, CaMV35S and cry1A and had good specificity and sensitivity. The limit of detection (LOD) of this biosensor was 0.1 nM without any signal amplification. Furthermore, our biosensor could be stably regenerated more than 100 times over at least 20 days and showed good reproducibility. This nucleic acid SPR biosensor has potential for application in other types of biological detection.

Comparative study on quantitation of human myoglobin by both isotope dilution mass spectrometry and surface plasmon resonance based on calibration-free analysis

The activity of proteins rather than the concentration of proteins in biopharmaceutical and in vitro diagnostics are often the primary focus. Nonetheless, development of a calibration-free concentration analysis (CFCA) approach that accurately quantifies the concentration of proteins based on molecular interactions with specific monoclonal antibodies and without the requirement of external calibrators would be beneficial to diagnostics. Generally, only analytes that interact with the antibody (Ab) are quantified by CFCA. Moreover, protein concentrations measured by CFCA usually vary when different Abs are used, and are lower than those obtained by amino acid analysis because any non-native state population of the target protein is not captured by the Ab. To achieve comparable results between CFCA and traditional amino acid analysis (AAA), an Ab that recognizes the target protein irrespective of its conformation should be used. In this report, three different monoclonal antibodies were used to quantify purified human myoglobin in solution by CFCA. The concentrations obtain by the Abs (i.e., 2.985, 2.912, 3.032 mg mL^-1) were comparable with that obtained by AAA. Moreover, isotope dilution mass spectrometry (IDMS) gave a human myoglobin concentration of 2.851 mg mL^-1, which is also in agreement with the results from CFCA. The performance of CFCA was evaluated by measuring various parameters, including within-day and between-day precision. The results demonstrated that the active concentration measured by CFCA is comparable with that of IDMS when the appropriate Ab is used. Recommended procedures for performing the new CFCA approach are provided. This study shows that CFCA represents a primary method for accurate protein concentration determination, which should aid the development of certified reference materials. Graphical abstract.

Certification and stability assessment of recombinant human growth hormone as a certified reference material for protein quantification

A certified reference material (CRM) for the quantification of protein, essential to manage quality control and quality assurance in protein-related works, has been developed. Amino acid analysis with conventional acid hydrolysis and isotope dilution HPLC-MS was used to establish an SI-traceable absolute protein quantification method using recombinant human growth hormone (hGH) as a model protein. The certification method was verified by comparative studies between 1) different methods of protein quantification based on microwave-assisted hydrolysis, and 2) different labs as part of the Asian Collaboration on Reference Material project with Japan, China, and Korea. Certification, evaluation of measurement uncertainty, homogeneity testing, and stability testing were carried out, after which the candidate CRM for hGH quantification was successfully certified with excellent agreement within the certified value in the two comparative studies. Although the quantification value of hGH by amino acid analysis showed good robustness in various conditions, results of intact protein analysis showed degradation profiles in temperatures higher than 4 °C. Consequently, storage and dissemination conditions should be set in accordance with stability tests. Based on the results, this method is believed to be suitable for accurate quantification of hGH. Additionally, it can also be used as a guide to preparation of CRM, and instructions for quality management of protein work for other similar proteins.