Overview
Our team developed a bacteria detection kit which is simple, effective and affordable for ordinary
families and lay people with emergency needs. In order to make our project more reasonable, we have
done a series of HP work. From the HP work, we have gained a lot of constructive suggestions to help
us clarify our thoughts. We finally chose specific ligands so that anyone who knows nothing about
biosafety can use our product safely. Our product detects bacteria using a specific receptor binding
assay, which is easy to operate and rapid.
Background
Through background surveys and field trips, we knew that food safety is a serious health concern.
First ever estimates of the global burden of foodborne diseases showed almost 1 in 10 people fell
ill every year from eating contaminated food and 420 000 died as a result.[1] Certain diseases, such
as those caused by pathogenic E. coli, are much more common in low-income countries, which have
highest burden of foodborne diseases.
Besides, current bacterial detection devices are generally for single pathogen detection, with no
detection tools for simultaneous detection of a bunch of the common foodborne pathogens, which makes
it more costly and inconvenient for individuals and organizations.
Figure 1: search results of “Bacteria detection kit” on a shopping platform[2]
End Users
Our designed bacterial detection kit provides a simple and inexpensive option to wide users requiring
no expertise in laboratory work. The product is suitable in home-based situation.
In terms of bacterial detection, physiological and biochemical identification require too many
instruments, serological identification has low accuracy, and the need for specialized instruments
for PCR is not affordable for the average family. In the home-based situation, it is reasonable to
use specific chromogenic reactions to detect bacteria. Therefore, we chose a molecular biological
identification method using safe chromogenic substrates and receptor magnetic bead complexes.
Product operation
Our product contains test tubes, a magnetic separator and a separation device. To allow consumers to
easily manage the test kit at home, each test tube contains four receptor binding
protein-nanomagnetic bead complexes (RBP-MBs) so that four common bacterial pathogens can be easily
isolated from the sample simultaneously. By simplifying this isolation procedure, we allow the price
of our product to be controlled at reasonable intervals. Our modeling team designed a separation
device to conveniently split the isolated bacteria solution in the test tube into four wells, each
containing a paper-based sensor with bacterial lysate and chromogenic substrate to detect one
specific bacterial pathogen.
According to Professor Ye's suggestion, we selected the central lattice that removed the sampling and modified
the hardware model into four reaction units to improve the detection rate and shorten the overall detection time.
It lays a foundation for the popularization of the device for detecting foodborne pathogens to life scenes
in the future.
Users need to turn the sample for detection into a fluid, place it into a test tube for separation by
the magnetic separator, discard the supernatant, resuspend the precipitate, and finally drop the
processed sample into the separation device. The treated sample flows into the four depressed sensor
wells of the device and test results are presented as color changes of the sensors which are
detectable by naked eye.
Figure 2: A model of the separation device for our detection kit (More information is available in
Hardware)
In order to precisely analyze the color signals of our paper-based sensors, our modeling group
developed a software called Image Colorimetric Detection (ICD) with the help of the research team
from South China University of Technology. Users can use ICD to calculate the concentration of the
bacteria in the sample. To use it, the user takes a picture, and selects a region of interest of the
picture. ICD gives the RBG values, including R, G, B, and IR,of the selected area (IR=blue
value). The bacteria concentration is calculated by the formula:
a1 and b1 is given in our
product, and IR is given by ICD.
Figure 3: App home page of Image Colorimetric Detection
Figure 4: Page for
detection results of Image Colorimetric Detection
Real-world implementation
In real-world implementation, the following issues need to be considered.
-
- The limit of detection (LOD)
- The limit of detection (LOD) of the device is around 106 CFU/mL, which is beyond the
limit for pathogenic bacteria in food in China. So, false negative test results are
quite common. We recommend the use of background color detection software, which is more
sensitive than the human eye, to confirm whether there is an alteration in color, since
there must be a large number of foodborne pathogenic bacteria as long as there are more
than 10 perturbations of the RGB values. In addition, it is better to take a picture on
a piece of white paper for RGB value detection, and avoid shadow in the picture to
reduce the error. Moreover, if there is an incubator and the deadline is more than one
day, culturing the sample will greatly improve the detection limit.
-
- Production cost
- Our detection reagents have not yet been manufactured in bulk and therefore the
production can be time consuming and costly. Regrettably, our products require lower
prices to be competitive. If produced in bulk, the fixed cost per unit can greatly
decrease, and extremely small doses of droppers can be applied and other unnecessary
reagents can be eliminated to control reagent cost and offset the high price of the
coupled magnetic bead complexes.
-
- Shelf life
- It is estimated that the test reagents can be kept for more than 6 months in the freezer
and 1 year on paper basis. However, at present, no experiments have been performed
regarding the change of the detection characteristics of the product especially the
sensors after several-month storage such as the detection limits. We suggest that, for
this class of bacterial detection devices, the best way is to buy it when needed, so
that there is no concern for prolonged shelf-life and the degradation of testing
performance. In addition, such reagents all need to be kept in a -20℃ freezer.
Safety
During the detection process, food-borne pathogenic bacteria may spread to other places as the sample
moves, causing secondary infection. We recommend that all operations for testing be performed at the
same place and that contact surfaces be disinfected when testing is completed.
Difficulties in generalization
Although our project is still in the prototype stage, we hope to understand how our detection device
performs on the market, and how this enormous demand had been ignored, to the point that no similar
product was commercially available.
We learned that pricing is a crucial element in deciding the usefulness of a test kit. Meanwhile,
from our public survey, we have learned that not many people are willing to spend this money, no
matter how competent they are to do so, because they think the odds are too small. The papers about
food safety awareness also corroborates the view.[3]
