Technology behind SensoGOLD™ Kits

SensoGOLD™ Platform Overview

SensoGOLD™ Bacterial Detection Kits are designed to detect the presence of bacterial pathogens based on their 16S rRNA signatures. 16S rRNA is a major component of bacterial protein making machinery and its sequence analysis has been well established in laboratory setting as a tool for microorganism identification.

Two types of SensoGOLD™ probes have been developed. The first type is designed to bind 16S rRNA region whose genetic sequence is highly conserved among the different microorganisms. These probes are activated by a wide range of bacterial species that include all major pathogenic microorganisms (see Figure 1). They are used in our Universal Bacterial Pattern Detection Kit, which are designed to screen for the presence of bacterial contamination, but not identify the specific pathogen. The second probe type was developed to bind variable regions of 16S rRNA whose genetic sequence differs between the microorganisms. Therefore, they are only activated by the presence of the specific bacteria. These probes are used in our Specific Bacterial Detection Kits, each of which is designed to detect a particular bacterial pathogen.

Figure 1: A detection probe that is chosen to target a highly conserved region will be activated by multiple bacteria. Such probe is optimal for screening for the presence of bacterial contamination, but cannot identify specific pathogen. A detection probe that is designed to target a variable region that is only conserved within the same miroorganism are useful to identify specific pathogen. Hiper-variable regions (black nucleotide letters in the figure) are not useful for detection since their nucleotide sequence varies even within the same microorganism.

SensoGOLD™ Kits provide a simple colorimetric output that can be read out with a naked eye. Nanoparticles in the test solution appear bright red when the target bacteria is present, but clump at the bottom of the tube when no bacteria is detected. Alternatively, the test solution can be spotted on the readout plates and the size and the color of the spot indicates the test outcome: red spot - bacteria are present, black spot - no bacteria are detected (see Figure 2). The readout plate with the test results can be stored at room temperature over long periods of time for later viewing or archiving purposes.

Figure 2: Left: photograph of readout tubes showing a positive sample and a negative control. Right: photograph of the readout plate with 6 positive samples (red spots, bottom row) and 6 negative controls (black spots, top row).

Molecular Details of the SensoGOLD Platform

Our SensoGOLD™ Platform combines the advances of nanoscale engineering with the unique physical properties of nanomaterials. The core of the system consists of gold nanoparticles, which are solid gold spheres 15 nm in diameter (around 10,000 times smaller than the width of the human hair). Gold nanoparticles are widely used in biomedical research due to their reproducible synthesis protocols, low batch-to-batch variability, low size variability and ease of conjugation of biological ligands. One critical property of gold nanoparticles is that they effectively absorb wavelengths of light associated with blue, yellow and green color spectrum. As a result, they appear brightly red in color, which is the major wavelength that is reflected from their surface. However, if individual nanoparticles are linked together into large molecular assembly structures, their absorbance profile shifts to absorb more red color. This results in clearly observed shift in the nanoparticle solution color from red to purple (see Figure 3). SensoGOLD™ platform makes use of this color changing properties of gold nanoparticles to generate easy to read colorimetric test results.

Figure 3: Colorimetric properties of gold nanoparticles. When dispersed, gold nanoparticle absorbance peaks at 520 nm, particles appear brightly red. When assembled, electromagnetic fields of nearby GNPs couple, absorbance peak red-shifts and particle color turns purple.

When 16S rRNA of the target pathogen is not present in the test sample, the gold nanoparticles in the SensoGOLD™ Platform are designed to self-assemble into supramolecular structures, indicated by the purple color of the solution. Short centrifugation spin at 1000g forces these structures to precipitate at the bottom of the test tube. In contrast, when target 16S rRNA molecules are present, they cause interference with the assembly process, resulting in gold nanoparticles that remain dispersed, indicated by the red color of the solution (see Figure 4). Small amount of the solution can be spotted on thin layer chromatography (TLC) readout plates (see Figure 2 above for the photograph of the plate with the detection spots). Cross-linked gold nanoparticles give black spots (indicates no pathogen is detected), while dispersed gold nanoparticles form red spots (indicating pathogen is present). The benefit of using the readout plate is that the plate with the results can be stored for later viewing or archiving purposes.

Figure 4: SensoGOLD™ assay schematics. When no pathogen is present in the test sample, gold nanoparticles form assembled structures, turning solution color purple. Small volume of solution is spotted onto readout plate to form a dark spot. Presence of the pathogen prevents gold nanoparticle assembly formation. Both the color of the solution and the readout plate spot remain red. 

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