Biosensors

Continuous Therapeutic Drug Monitoring

Continuous drug monitoring has the great potential to improve the precision medicine by providing real-time information about an individual's response to therapeutics. It allows immediate clinical decision by clinicians to the patients and precision control of drug concentrations within its narrow therapeutic window more frequently than before. Regular therapeutic drug monitoring, as we all know, relies on blood samples typically collected at peak, trough and intermediate points for measurement, which is painful, cumbersome and lacking of real-time feedback (Figure 1). Continuous drug monitoring has been recently achieved by state-of-the-art technologies such as electrochemical aptamer-based sensors, wearable sensors and implantable sensors. At CENBRAIN, we aim to develop aptamer field effect transistors-based sensors capable of real-time, and in high potential achieving continuous, of monitoring of drugs in clinical samples.


Figure 1. Current practice of therapeutic drug monitoring and its limitation.


Biosensors for Disease Diagnostics

Right now, the detection of COVID-19 is largely limited to hospitals and CDCs (Center for Disease Control and Prevention). The mainstream technology is Nucleic Acid Amplification Test (NAAT)-based Polymerase Chain Reaction (PCR), which requires costly equipment, clean lab environment and trained personnel. No feasible technology can screen infected people among a large crowd. Recently, some technological companies have proposed lateral flow strips for fast on-site detection without using bulky equipment, such as immunoassay strips and isothermal NAAT strips. Immunoassay based on antibody-antigen reaction is preferred for point-of-care detection since it doesn’t require nuclei acid extraction and amplification which tends to be polluted by environmental impurities. However, immunoassay strips are limited in sensitivity since it relies on inaccurate reading of colors provided by gold colloid or nanoparticles. An efficient technique for fast on-site detection of COVID-19 with high-sensitivity (preferably comparable with mainstream PCR) detection, ease of operation and field deployment capability is urgently needed.

Our goal in this project is to design and implement label-free reusable biosensors for accurate point-of-care detection of COVID-19 from pharynx swab samples. It uses immunoassay technique and the sensitivity should be close to mainstream bulky PCR-based technology. Programmable nanoporous structure is the core of proposed biosensor. The operation after pharynx swab sampling should be completed within 15 minutes, and the whole system can be deployed in the field. Working prototypes demonstrating the principle-of-operation of the biosensor and related needed user interfaces. The sensitivity for COVID-19 should reach fg/ml level (or 100 pfu/ml). The workflow after pharynx swab sampling until results output will be established, which should be completed within 15 minutes. The proposed biosensor has complementary electrical and optical signatures, which avoid electromagnetic interference of signals and differentiate target analytes of similar dielectric constant but different optical coefficients.

As shown in Figure 2, a biosensor based on nanoporous materials has been prepared. The basic material of the sensor is a nanoporous material, and its surface is gold-plated, so that LSPR and F-P interference can act simultaneously to improve the sensitivity. The sensor is packaged in a PDMS microfluidic chip, so that the liquid driven by the syringe pump is automatically delivered to the sensor surface for detection.

Based on the biosensor, the gold-plated nanoporous material is biofunctionalized, and the ACE2 binding protein is solidified on the sensor surface in the form of a covalent bond. The technical route is shown in Figure 3.

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Figure 2. Biosensor based on nanoporous materials: (a) Nanoporous material sample; (b) Nanoporous material encapsulated in PDMS microfluidic chip; (c) SEM top view of nanoporous materials, with diameter 250nm and spacing 400nm; and (d) SEM side view of the nanoporous material, with thickness 1um.



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Figure 3. Biosensor’s bio-functional process.

After gold plating, the nanoporous film has both F-P (Fabry-Perot) interference and LSPR (Localized Surface Plasmon Resonance) interaction, which is very sensitive to the binding of surface biomolecules. Based on this mechanism, a detection method for measuring the reflection spectrum of the biosensor by a portable optical fiber spectrometer is established. Figure 4 shows a portable fiber spectrometer Ideaoptics PG-2000 used to detect the reflection spectrum of a biosensor.



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Figure 4. (a) Optical fiber spectrometer, including spectrometer, light source, Y-type optical fiber, optical fiber probe, sample box, etc; (b) Optical fiber probe, sample box and biosensor; (c) A schematic diagram of the response of the biomolecule solution flowing through the surface of the biosensor in real-time optical detection; and (d) Schematic diagram of the sample box in connection with microfluidic system.

Based on the sensor and its detection system, the S1 protein of the new coronavirus COVID-19 is used as a specific antigen to conduct a biological detection test. The detection is carried out in the range of 40pM to 5nM in terms of S1 protein concentration. The data obtained are shown in Figure 5. It can be seen that the higher the S1 protein concentration, the larger the red shift of the spectrum. "Super Blocking" refers to the case where the S1 protein concentration is zero. The 5nM data point is blue-shifted compared to the 1nM data point. This is because the sensor sample accidentally fell to the ground when detecting the 5nM concentration, and a part of the biological material was removed from the sensor surface, so the peak of the reflection spectrum is blue-shifted.

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Figure 5. Reflectance spectra of biosensors with different S1 protein concentrations.