Low-cost screen printed carbon sensors are being used to rapidly detect bacteria commonly found in wounds, which could pave the way for a real-time medical device.

In a study by the University of Strathclyde and NHS Ayrshire & Arran, researchers used sensitive portable electrochemical sensors, which detected infections in clinical samples within 30 minutes — much quicker than current hospital laboratory testing.

The detection of infection in clinical practice can be expensive and typically takes at least 48 hours for gold-standard laboratory methods of wound infection detection and bacterial identification.

In a collaboration with NHS Ayrshire & Arran clinicians, dressings and swabs were collected from patients with diabetes-related foot ulcers at the University Hospital Ayr. These samples were then measured at the University of Strathclyde using the novel sensor, and found the bacterial infection could be rapidly detected. 

In the preliminary work, the sensors were used to detect Proteus mirabilis, one of the most common bacteria types found in wounds. This organism is commonly found in the human gastrointestinal tract and forms part of the body’s normal microflora, but can cause disease in those with compromised immune systems or wounds.

The peer reviewed study, which won Best Paper Award at the annual World Congress on Electrical Engineering and Computer Systems Science in July, describes the real time electrochemical detection of the pathogen, with the growth detected in laboratory tests an hour after sample inoculation.

The electrochemical technique adopted measures that show the electrical “impedance” of a sample over a wide range of electrical signal frequencies — creating spectra — formed by the measurement of how current flows through the bacterial layer at each frequency. Changes to these spectra over time can be investigated, providing information about the microbiological content of the sample. The process and mathematical approach used to study the spectra ultimately paved the way for patents.

Healthcare associated infections (HAI) are a significant threat to patient welfare, resulting in increased treatment times, costs, and illness.  Wound infections are a common form of HAI.

“Diabetes foot ulcers are, unfortunately, common, with the lifetime risk for an ulcer being approximately 15-25%,” says Consultant Diabetologist for NHS Ayrshire & Arran Andrew Collier, BSC (Hons), MBChB, MD, FRCPE, FRCSPG, was a part of the study, along with senior podiatrist Danielle Main. “Infection is common and can lead to lower limb amputation if not treated early and aggressively. Early detection and appropriate treatment of infection will reduce the risk of amputation significantly, with three out of four amputations preventable. The early detection of infection demonstrated in this study will have significant impact upon both the individual with a diabetes foot ulcer and NHS resources.”

A research study commissioned by the Scottish government that was published in June, and involved Strathclyde, suggested 1% of patients develop hospital associated infections (HAIs), costing NHS Scotland more than £46M ($66 million) annually.

The researchers believe the technology has the potential to be incorporated into a cost-effective, real-time wound monitoring device — able to rapidly detect infection — which could greatly reduce wound infection detection and identification times in clinical settings.

“While a range of other bacteria have been detected using electrochemical impedance spectroscopy, to the best of our knowledge this is (the) first reported study of real-time Proteus mirabilis detection using a label-free, screen-printed carbon electrode,” says Aiden Hannah, a biomedical engineering researcher from the University, who worked on the study. “The ability of our low-cost sensors to rapidly detect the presence of infection in clinical wound samples, highlights their potential for adoption into point-of-care infection monitoring devices. The ability to monitor infection status in real-time, would enable earlier intervention and improved prognosis.”