Bioaffinity Based Biosensor and immunosensor

Oxford Univ Begbroke Science Park




Bioaffinity Based Biosensor and immunosensor


Biosensor is a detection device with high analytical specificity made of layers of biological elements with biorecognition quality that are immobilized on a substrate having reversible interactions with the analyte and a signal transducer.

Immunosensors are biosensors that have antibodies as biological element.



AFM functionalised tip as force sensor
AFM’s functionalised tip with eg. biotin
The force of adhesion due to rupture can be calculated from deflection measure


Self assembled monolayers SAMs

SAMs are long chain monolayers of diverse functionalities organised on surface of noble metals or SiO2 for use as sensor arrays
Two main coupling schemes
thiol coupling
silane coupling



Advantageous techniques for characterisation of self-assembled monolayers SAMs

-ToF SIMS with elemental and molecular fingerprinting; detect distribution and location of biomolecules

-Tip enhanced Raman Spectroscopy, FT-Raman Spectroscopy for molecular recognition

-AFM tapping mode for imaging biofunctionalised surfaces, high resolution, ability to operate in liquid medium, topographical information, images of individual molecule measure molecular dimensions

-AFM as force sensing tool; AFM with functionalised tip, f-d mode probes functionality, elastic property, adhesion strength, and range of inter-atomic/molecular interactions for molecular recognition

-XPS complemented with Ellipsometric and contact angle measurement can confirm the presence of immobilized molecules

Time of Flight SIMS

SIMS secondary ion mass spectroscopy analyses mass of ions and molecular fragments ejected from surface (dept of 10-20 Å)

TOF-SIMS uses pulse primary ion beam at low fluence to ionize and desorbe the sample surface

ToF analyzer detects time of flight of secondary ions to mass spectrometer having different velocities

Mass spectrum counts of secondary ions emitted to determine molecular species.

Highly focused primary ion beam (ca 1 μ dia ) images visualising molecular distribution on the surface


MICROCANTILEVERS AS BIOLOGICAL SENSORS

Microlever Dynamic mode in micro balance method (resonance due to oscillation) measures resonant frequency changes due to added mass

Microlever Static mode in surface stress method (deflection due to bending) mode measures deflection of lever, displacement of the tip due to changes of stress or mass loading (operates both in air and liquid)


Refs:

Myhra S (Oxford Univ), A review of enabling technologies based on scanning probe microscopy relevant to bioanalysis, Biosensors and Bioelectronics, Volume 19, Issue 11, 15 June 2004, Pages 1345-1354

Bruno Pettinger, Tip-enhanced Raman scattering: Influence of the tip-surface geometry on optical resonance and enhancement, Surface Science 603 (2009) 1335–1341

Thomas Ederth (Oxford Univ), Computation of Lifshitz-van der Waals Forces between
Alkylthiol Monolayers on Gold Films, Langmuir 2001, 17, 3329-3340