Self-assembled monolayer (SAM) of n-alkanethiols of different chain lengths (n ¼ 2, 3, 6, 11, 16) on a gold surface are used to immobilize antibodies which in turn bind to a antigen. The antibody and antigen used in this study have similar molecular weights i.e. $150 kDa. The antibody [1.5 mg cm À2 ] immobilized varied with the surface packing density of the SAM of carboxylic acid-terminated n-alkanethiols of different lengths. In comparison, the efficiency of antibody immobilization was lowest on the loosely packed SAM of n-alkanethiols (n # 3) and the highest on the densely packed SAM of n-alkanethiols (n $ 11). However, increased immobilization of antibodies with increasing chain length of the n-alkanethiols [n > 11], did not result in a corresponding increase in antigen binding. An attempt to explain this phenomenon based on packing density and an orientation of the captured antibody is presented.www.rsc.org/advances 80480 | RSC Adv., 2015, 5, 80480-80487This journal is
The article reports a proof of concept validation of bacterial detection using Siderophores. Desferrioxamine B (DesfB) was used as the Siderophore to capture Escherichia coli on gold coated microcantilever surface. Self-assembled monolayer based gold thiol chemistry was used for surface functionalization of the Siderophore on top surface of the microcantilever. The bacterial attachment to the siderophore was observed through Fourier Transform Infrared Spectroscopy (FTIR) and Fluorescence Microscopy. The DesfB coated surface allows only the live bacterial cells to be attached and it is evident through the FTIR band formation. In a mixture of live and dead E. coli cells, the Fluorescence Microscope image indicates green emission from live cells and a core-shell structure formation upon progress of time. For a sample dilution of 10 −1 , the mass change of live E. coli bonded to Siderophores is four times higher than that of dead cells and 12 times higher to that of negative control on microcantilevers. Therefore this study should be considered as a foundation to build a miniaturized biosensing platform to distinguish between bacterial or viral infections in real time. The proposed platform could differentiate between bacterial and viral infections thus rendering it as Point of Care (PoC) diagnostic tool aiding Internet of Things (IoT) applications.
Cantilevers immersed in liquid experience viscous damping and hydrodynamic loading. We report on the use of such cantilevers, operating in the dynamic mode with, (i) frequency sweeping and (ii) phase locked loop methods. The solution to reliability issues such as random drift in the resonant peak values, and interference of spurious modes in the resonance frequency spectrum, are explained based on the actuation signal provided and laser spot size. The laser beam spot size and its position on the cantilever were found to have an important role, on the output signal and resonance frequency. We describe a method to distinguish the normal modes from the spurious modes for a cantilever. Uncertainties in the measurements define the lower limit of mass detection (mmin). The minimum detection limits of the two measurement methods are investigated by measuring salt adsorption from phosphate buffer solution, as an example, a mass of 14 pg was measured using the 14th transverse mode of a m × 100 μm × 1 μm silicon cantilever. The optimized measurement was used to study the interaction between antibody and antigen.
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