DeTectUs 2019

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Contents

DeTectUs 2019

DeTectUs is a team from the Technical University of Denmark competing in the SensUs 2019 event. For SensUs 2019, AdUp Sense investigated the possibilities for creating a biosensor which is able to measure the concentration of Adalimumab. The full TRD can be found [ via this link]

Method

Surface plasmon resonance (SPR). The refractive index of the sample is measured which is then correlated to a calibration curve, responding to a specific concentration of adalimumab. Gold surface modification with a linker type molecule and an engineered antigen against adalimumab on top is utilised. This system is capable of capturing adalimumab which is then detected by SPR.

Molecular Recognition

Four peptides mimicking the site of interaction of TNF alpha with adalimumab were engineered. The gold surface of the sensor was functionalized with a self-assembled monolayer composed of 3-Mercaptopropionic acid (MPA). After activation of the carboxylic acid of MPA with N- (3-Dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS), the peptides were attached via an amide bond. The free carboxylic acid residues were

furthermore blocked with ethanolamine. 

Physical Transduction

SPR are oscillating electromagnetic waves of conduction electrons on the interface between a metal and dielectric. The conduction electrons have a resonant frequency at which they are excited, leading to these oscillations. As resonance is a requirement, only certain energies can excite the plasmons. This is done by matching the momentum of a Transverse Magnetic oscillation (polarised light) to the oscillation of the plasmons. When this coupling happens, SPR waves propagate along the surface of the metal film, gold in this case, and exponentially decays parallel to the surface.

As light coming from the medium of air cannot match the momentum of the plasmons by itself, the SPR is only possible with a coupling mechanism: using a higher refractive index material on one side of the metal than the other. Prisms are commonly used as they have this higher index.

In this biosensor, the Kretschmann configuration is used.

A different concentration of adalimumab means a change in the refractive index of the analyte, leading to a change in the SPR excitation angle.

Optimisation of the optical setup can be done using several parameters such as the metal layer, the RI of the coupling materials (prism and substrate), focal length of focusing and collimating lens, and the length between the CCD detector and the final collimating lens.

Cartridge

There is no cartridge system. The chip will be placed directly on the prism by hand, as will the plasma.

Reader Instrument

The Setup has a dimension of 470x300x100 mm and can change the angle of the camera and laser from 35-85 degrees, being able to measure in water and air. The setup uses thread and bolts to change the angle of the setup; The thread and bolt has a self-locking ability when sufficient axial load is applied and the axial load on the bolt minimizes slack in the system which allows for changing the setup in small steps increments.

The user would have to pipette the plasma on the chip. To increase accuracy, the user could create an turbulent environment for the plasma by repeatedly pipetting the plasma in and out of the pipette. Then the chip can be put on the prism to measure the concentration of adalimumab.