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Ultra-sensitive paper-based diagnostics

Loop-mediated isothermal amplification and silver nanoplates allow for single copy detection of MRSA

Accurate testing for infectious diseases has long been a focus for both researchers and medical professionals. Whether in a pandemic or delivering routine care to remote locations, access to quick and efficient diagnostic tests is the first step to treatment. Ideally such tests are inexpensive and do not require the use of special instruments, yet maintain the high accuracy and sensitivity of more complex lab-based tests.

Akkapol Suea-Ngam and colleagues from the de Mello Group and Chulalongkorn University have made such a test using a new gene-detecting colorimetric strategy. Significantly, the team were able to detect the presence of DNA from methicillin-resistant Staphylococcus aureus (MRSA), the antimicrobial resistant bacterium responsible for MRSA infections. The test relies on loop-mediated isothermal amplification (LAMP) of the DNA, a technique which allows for efficient target amplification without the need for multiple thermal cycles. DNA amplification was combined with a silver nanoplate/sodium bromide system detection system. Upon exposure to the bromide salt, silver nanoplates change their geometry, and thus their color. However, if present the amplified MRSA DNA acts as a protecting layer on the silver plates and inhibits the color change. This entire system is patterned onto a simple cellulose substrate for easy and inexpensive manufacture.

The test results can be read out two different ways; either using a smartphone camera for a quantitative readout or visually for a qualitative assessment of the presence of MRSA DNA. Importantly, the authors note that this system can be modified to detect any DNA target by simply switching the LAMP primers.

The ease of use, sensitivity and flexibility of this system directly address the needs of healthcare professionals in performing rapid point-of-care diagnostic testing.

Written by Nathan Khosla

Read the full paper here

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