A visual chip-based coimmunoprecipitation technique for analysis of protein-protein interactions

A simplified direct on-chip forward or reverse immunoassay for evaluating protein-protein interactions in the serum

BACKGROUND

The identification of protein-protein interactions is a great challenge. In this study, we fabricated a gold surface-modified biochip with activated sophorolipids (SLs) in combination with 16-amino-1-hexadecanethiol hydrochloride to detect serum proteins.

MAIN METHODS AND MAJOR RESULTS

The on-chip immunoassay reported here included a forward assay, in which a ligand is immobilized on the biochip surface and allowed to interact with its free specific receptor in liquid phase, and a reverse assay, in which a receptor is loaded on the biochip surface and combined with its free specific ligand in solution. The specificity of the molecular interactions on the biochip was evaluated using immunological blocking assays and chemiluminescent immunoassays (CLIA). Hemophagocytic lymphohistiocytosis (HLH) serum was used to test the potential utilization of the biochip. Reverse receptor CD25-based interleukin (IL)-2 and forward ligand IL-2-based CD25 assays revealed that the limit of detection of the target proteins was as low as 156 and 78 pg/ml, respectively. Using receptor- or ligand-based platforms, we found that the positive rates of free IL-2 and soluble CD25 (sCD25) monomers in the sera of HLH patients were 14.3% and 71.4%, respectively. In addition, the biochip showed good compatibility with CLIA for the measurement of sCD25 (r = 0.77, p < 0.01).

CONCLUSIONS AND IMPLICATIONS

Biochip platforms, such as on-chip immunoprecipitation (IP), can be used to evaluate the interactions between proteins, ligands, and receptors, or enzymes and substrates in serum.

Detection of antibodies against avian influenza virus by protein microarray using nucleoprotein expressed in insect cells

Avian influenza (AI) is an infectious disease caused by avian influenza viruses (AIVs) which belong to the influenza virus A group. AI causes tremendous economic losses in poultry industry and pose great threatens to human health. Active serologic surveillance is necessary to prevent and control the spread of AI. In this study, a protein microarray using nucleoprotein (NP) of H5N1 AIV expressed in insect cells was developed to detect antibodies against AIV NP protein. The protein microarray was used to test Newcastle disease virus (NDV), infectious bursal disease virus (IBDV), AIV positive and negative sera. The results indicated that the protein microarray could hybridize specifically with antibodies against AIV with strong signals and without cross-hybridization. Moreover, 76 field serum samples were detected by microarray, enzyme-linked immunosorbent assay (ELISA) and hemagglutination inhibition test (HI). The positive rate was 92.1% (70/76), 93.4% (71/76) and 89.4% (68/76) by protein microarray, ELISA and HI test, respectively. Compared with ELISA, the microarray showed 100% (20/20) agreement ratio in chicken and 98.2% (55/56) in ornamental bird. In conclusion, this method provides an alternative serological diagnosis for influenza antibody screening and will provide a basis for the development of protein microarrays that can be used to respectively detect antibodies of different AIV subtypes and other pathogens.

A simple 96 well microfluidic chip combined with visual and densitometry detection for resource-poor point of care testing

There is a well-recognized need for low cost biodetection technologies for resource-poor settings with minimal medical infrastructure. Lab-on-a-chip (LOC) technology has the ability to perform biological assays in such settings. The aim of this work is to develop a low cost, high-throughput detection system for the analysis of 96 samples simultaneously outside the laboratory setting. To achieve this aim, several biosensing elements were combined: a syringe operated ELISA lab-on-a-chip (ELISA-LOC) which integrates fluid delivery system into a miniature 96-well plate; a simplified non-enzymatic reporter and detection approach using a gold nanoparticle-antibody conjugate as a secondary antibody and silver enhancement of the visual signal; and Carbon nanotubes (CNT) to increase primary antibody immobilization and improve assay sensitivity. Combined, these elements obviate the need for an ELISA washer, electrical power for operation and a sophisticated detector. We demonstrate the use of the device for detection of Staphylococcal enterotoxin B, a major foodborne toxin using three modes of detection, visual detection, CCD camera and document scanner. With visual detection or using a document scanner to measure the signal, the limit of detection (LOD) was 0.5ng/ml. In addition to visual detection, for precise quantitation of signal using densitometry and a CCD camera, the LOD was 0.1ng/ml for the CCD analysis and 0.5 ng/ml for the document scanner. The observed sensitivity is in the same range as laboratory-based ELISA testing. The point of care device can analyze 96 samples simultaneously, permitting high throughput diagnostics in the field and in resource poor areas without ready access to laboratory facilities or electricity.