Folded paper sensors to monitor pandemics

Origami-paper sensors to identify biomarkers in wastewater have been developed at Cranfield University, UK.

The researchers say the test device is low-cost and fast and could dramatically change how public health measures are directed in a future endemic/pandemic.

Testing wastewater is one of the primary ways to assess the prevalence of infectious diseases in populations.

By taking samples from various water treatment plants across the country, researchers can find out which areas have the highest infection rates. This method was used in the COVID-19 pandemic to track community infection rates and direct public health measures.

The team notes that, until now, the most accurate way to test wastewater samples has involved the polymerase chain reaction (PCR) test, which must be conducted in centralised laboratories by well-trained personnel.

The samples are collected, stored and transported in a cold chain to the lab, before they can be processed, which can take multiple days and is relatively expensive.

Loop-mediated isothermal amplification (LAMP) has emerged as an alternative method for detection of pathogens.

The paper, on Paper microfluidic sentinel sensors enable rapid and on-site wastewater surveillance in community settings, explains how LAMP provides 'a less complex assay workflow by negating the demand for complex thermocycling equipment'.

The combination of LAMP-assay-based paper microfluidic devices and wastewater-based epidemiology are, in turn, gaining traction for point-of-need diagnostics, shares the paper in Cell Reports Physical Science.

The new sensor is reported to be rapid, user-friendly and portable.

Wastewater samples are placed onto a wax-printed paper sheet, which is folded in an origami style. The method comprises 'a simple hand-held syringe-based sample preparation system to enrich the pathogen samples from wastewater, enabling the extraction, purification, amplification and in situ detection'.

Chemicals in the paper react to certain disease markers, triggering a fluorescent colour to emerge. The results are illuminated using a handheld UV torch and can be read using a mobile phone camera.

More specifically, primers and enzymes for specific and sensitive LAMP assays are contained in the paper to identify certain target sequences of disease markers, shares Zhugen Yang, Professor of Biosensing and Environmental Health at the University.

He explains that the paper device is folded to enable nucleic acid introduction, washing and elution according to the origami design. 'By folding-unfolding, it can [make the] sample purification ready for amplification, but without need of any power and centralised facilities.'

'The optimal pore size, channel width and channel length of the paper device were concluded to be 4.0mm, 1.5mm and 2.5mm, respectively,' reads the paper.

According to the team, the test can be used for any type of wastewater sample to detect SARS-CoV-2 for COVID-19, influenza, and infectious diseases such as TB, malaria and HIV.

Yang developed the sentinel sensors as part of the national COVID-19 wastewater surveillance programme. In 2021, he conducted field tests at four quarantine hotels around Heathrow Airport. The whole process took under 90 minutes in a hotel basement using a digital bath and syringes, while a PCR test on wastewater takes around four hours.

The new sensors were found to be at least as accurate as the PCR test. This is especially useful for areas with limited resources.

Yang says, 'This could be a real game-changer when it comes to predicting disease rates and improving public health in the face of future pandemics.'

They think the sensors could be used for a couple of years if stored correctly in a dry place.

While an unstable temperature may affect sample quality, this can purportedly be minimised through standardised sample processing and purification, by using a portable constant temperature box.