Possibilities in Diagnostics Thanks to Miniature Flow Sensor

The trend towards near-patient lab diagnostics (POCT or point-of-care testing) continues to grow in medical diagnostics. The idea here is that testing should take place as promptly as possible, preferably directly at the patient’s bedside. Precise microfluidic systems are required for more difficult examinations.

A urine test using a paper strip is one famous example of a POCT. In these tests, the different components of urine—such as white and red blood cells, the pH value, and glucose—create color changes on the reactive surfaces of the test strip. The nurse will be able to determine qualitative information about the concentration of the different substances in the sampled urine by comparing the color patterns to a reference scale.

In a much simpler exemplary procedure, it is possible to non-invasively determine the oxygen saturation of blood via the skin by clipping an optical sensor to the patient’s fingertip. Earlier, before the advent of these pulse oximeters, a blood sample was actually taken and then sent to the central lab for testing.

More difficult tests—for instance, to detect specific bacteria or viruses continue to depend on the specialist personnel and elaborate infrastructure of a central laboratory. Such tests frequently need additional steps in terms of pre-treatment or sample preparation, complex devices for analysis, or special temperature conditions.

In order to perform these tests directly at the patients’ bedside in the hospital, it is essential to simplify the test procedures and minimize the interaction with the user. In ultimate cases, the entire test is performed independently on a single microfluidic system; that is the entire ‘lab’ is incorporated on a chip and thus becomes a ‘lab on a chip’.

Microfluidic POCT

In recent years, an increasing amount of research has been executed in the field of microfluidics, especially in the biosciences, in order to miniaturize and automate lab experiments, (bio)chemical processes, and diagnostic tests. Instead of pipetting discrete quantities of liquids from one container to another, today the liquid in a microfluidic system flows via the small channels of a manifold.

Usually, the liquid in these channels is moved by external pumps or pressure sources to which the fluidic chip is connected. The flow rate is measured using flow sensors in order to stabilize the flow generated by the pump or control the applied pressures. Thanks to their exceptional sensitivity even at very minimal flow rates, Sensirion’s microthermal mass flow meters for liquids set the industry standard in the precise monitoring of liquid flows in microfluidic systems.

The dimensions of the channels in the fluidic system have been considerably reduced down to the micrometer range, with the liquid volumes in the microliter or even nanoliter range. This allows the microfluidics to significantly decrease the sample and reagent quantities and enable quicker reactions, thus increasing throughput.

Additionally, the smaller size of the fluidic system also means lower costs and smaller devices. Both are essential conditions in order to perform tests in a decentralized manner directly at the place of care; that is, at the bedside, on the same hospital floor or in a doctor’s office. This indeed results in simplifying the logistics and provides quicker results for improved and more targeted treatment of patients.

Possible Applications in Medical Technology and Other Fields

Microfluidic POCT devices that are commercially available can be used for applications like measuring proteins used as biomarkers in the diagnosis of heart attacks. Other devices examine blood samples in order to determine the composition of red and white blood cells and their subtypes.

Cytometry is another application in medical technology that determines the concentration of T helper cells whilst monitoring the immune systems of AIDS/HIV patients. Finally, efforts are being made to transfer molecular-biological methods for the detection of, for example, antibiotic-resistant bacteria through their DNA to point-of-care systems. It is also possible to develop genetic fingerprints for forensic purposes using POCT devices.

However, microfluidics plays a very important role in areas other than the clinical field, such as industrial process monitoring and research and development. Microbiology, in particular, is completely critical today in the drinks and food production sector; it is used for monitoring the quality of yeast cells that ferment malt to beer, and the bacterial populations in milk, which must not surpass specific threshold values.

Previously, discrete samples were diverted from the production process and sent to laboratories for analysis; now latest types of miniaturized flow cytometers allow direct verification of individual production lots or even nonstop monitoring on the production line.

Improved Performance through Precise Flow Monitoring

POCT devices

POCT device

The field of microfluidics, because of its origins, is closely linked with the biosciences and related technologies, such as cell manipulation, cell sorting, and DNA analysis. Microfluidics is also relevant in several other miniaturized systems that use liquids; for instance, microscopic chemical reactors and micro fuel cells for portable energy generation.

In all these developing application areas, the accurate monitoring and control of liquid flows is vital for the reliable operation of the respective device. With a small form factor of just 10 x 10 mm2, Sensirion’s LPG10 flow sensor offers exceptional precision and speed in the measurement of flow rates that are extremely low. The sensor is available with a planar microfluidic glass substrate and enables extremely compact integration in any fluidic system.

The established microthermal measurement method in a groundbreaking design enables flow measurements of only a few milliliters down to single microliters per minute, or even lower. Glass, as the only wetted material, ensures optimal compatibility with pharmaceutical and biological processes.

The sensor provides a highly precise and direct measurement of the flow rate at every significant point in the fluidic system. The reliable detection of common errors such as air bubbles, clogging or leaks is indeed incorporated.

All images sourced and provided by Sensirion

About Sensirion Inc


Medical devices must meet the highest standards in terms of quality and reliability. Doctors, nurses, and patients benefit daily from applications in the field of medical technology that are getting smarter by the day.

The use of proven Sensirion sensor solutions contributes to this and offers the possibility of making applications safer, more reliable and more convenient. Our many years of experience in the field of medical technology make us the preferred experts for leading medical-technology companies.

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Last updated: Jun 6, 2023 at 8:43 AM


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