Point-of-Care Applications

Point-of-care testing (POCT) enables doctors to detect and diagnose diseases at or near the patient's site at a faster rate than traditional laboratory-based tests. There are many point-of-care (POC) diagnostic devices on the market, including but not limited to glucose monitoring, pregnancy/infertility testing, infectious disease testing, cholesterol testing, as well as heart markers.

With the development of POC diagnostic devices, it is possible to perform such identification in remote areas or places where medical laboratories cannot be accessed. The integration of microfluidic technology in POC enables fluid manipulation and detection in a single device with minimal sample requirements.

Characteristics of An Ideal POC Device

Generally, an ideal POC tool should have the following characteristics:

• Real-time analysis: The point of an ideal POC device is to be able to analyze samples in real-time at the point of care.
• High sensitivity: The ideal POC device should be highly sensitive to capture and detect very small amounts of target components or pathogens.
• Fast sample-to-results turnaround: For pathogens, rapid detection of POC systems can benefit patients from early intervention and improve survival. Similarly, in environmental applications, quick results can help take necessary measures as quickly as possible.
• Integrable: The technology needs to be integrated with various modes, such as readers or communication systems.

Microfluidics in Point-of-Care Devices

Most routine diagnostic methods involve culturing cells to harvest enough pathogens for detection. Since POC diagnosis should be performed quickly, molecular diagnostic techniques that do not involve cell culture are preferred. However, the currently used techniques involve many sample preparation steps and are very time-consuming, such as PCR and ELISA. These technologies need to be miniaturized and integrated into a single chip that can perform all sample preparation steps, measurement, detection, and analysis.

The unique features of microfluidic diagnostic chips make these microchips suitable for immediate care applications, such as modularity, portability, low reagent and sample consumption, and high sensitivity. These microfluidic point-in-time chips are very sensitive and can handle very small amounts of samples. If necessary, it can be modified or parallelized to analyze larger quantities.

Fig.1 Scheme of a microfluidic-based POC diagnostic system integrated into a hand-held device. (Jung W, et al. 2015)

Microfluidic POC Device for Infectious Disease Detection

Microfluidic POC diagnostic equipment usually relies on antibodies for rapid and effective bacterial identification. The advantages of mixing nanoparticles with microfluidic systems are that they reduce the volume of samples and reagents required, and have better sensitivity and faster processing. Currently, a microfluidic-based POC system has been developed to combine functionalized nanoparticles and microfluidic technology to detect foodborne pathogens such as Salmonella, Listeria, Cholera and E. coli. This combination is often used for optical detection.

Fig.2 Microfluidics-based SPR biosensor that can be used for bacteria, DNA or protein detection. (Pires N, et al. 2014)

Whether it is fluorescence, colorimetry, SERS or Raman spectroscopy, the type of signal collected during the optical detection process depends on the material properties of the probe. For example, quantum dots can be functionalized with antibodies specific to specific bacteria or viruses, and then form a "sandwich-like" complex with the target analyte. The number of pathogens can be inferred from fluorescence recording. In other cases, surface plasmon resonance (SPR) detection methods are used with gold-plated microfluidic channels and immobilized antibodies for selective bacterial detection.

Besides, a simple colorimetric method can be used to achieve optical detection by the naked eye. When the chemical reaction after capturing the analyte results in a visible color change, colorimetric determination can be performed. Since the peak of the absorption wavelength changes when the particles are gathered, it can be achieved by using plasmon nanoparticles.

Microfluidic POC Device for Environmental Testing

Sample Preparation

Sample preparation steps can include concentration or dilution, separation, buffer exchange, extraction, and reaction. The POC chip may need to integrate any combination of them to be fully automated. According to the target material, the appropriate sample preparation technique can be selected.

Detection

The integrated capabilities of microfluidics allow multiple detections and sensing methods to be used for microfluidic-based instant medical applications.

• Electrochemical Sensing: Contact electrodes and non-contact electrodes can be integrated with the microfluidic chip. By measuring the voltage/current output, the presence and concentration of the required chemicals can be monitored in real-time.
• Optical Measurements: Fluorescent labels are usually used in immunoassays, which can be used for high sensitivity and specific targeting of biological analytes. Chemiluminescence is excellent in detecting compounds.

The use of microfluidic chips can capture a variety of chemicals, toxins, and microorganisms in environmental samples, such as aldehydes, lead (II), gold (III), iron (III), nitrite, chromium (VI), promethazine, Polycyclic Aromatic Hydrocarbons, E. coli, etc.

References

• Jung W, et al. (2015). "Point-of-care Testing (POCT) Diagnostic Systems Using Microfluidic Lab-on-a-chip Technologies." Microelectronic Engineering. 132: 46-57.
• Pires N, et al. (2014). "Developments in Optical Detection Technologies in Lab-on-a-Chip Devices for Biosensing Applications." Sensors. 14: 15458-15479.

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