Biomolecule sensing

Niwa D, Omichi K, Motohashi N, Homma T, Osaka T (2006) Organosilane self-assembled monolayer-modified field effect transistors for on-chip ion and biomolecule sensing. Sens Actuator B 108 721-726... 

Initially, fiber ends were conjugated with biomolecule sensing layers and dipped into test tubes while reactions occurred and were monitored with photomultiplier tubes (PMTs). These types of devices are called fiber-optic biosensors (FOB) and are not performed on-chip. Many experiments and devices were developed throughout the 1990s using FOB techniques [4]. 

V.P. Drachev, V.M. Shalaev, Biomolecule sensing with adaptive plasmonic nanostructures, in Surface-Enhanced Raman Scattering Physics and Applications, vol. 103, ed. by K. Kneipp, M. Moskovits, H. Kneipp (Springer-Verlag, Berlin Heidelberg 2006), pp. 351-366 (Top. Appl. Phys.)... 

Figure 39 Representative structure and energy diagram of a flexible PLED integrated with the biomolecule sensing element and the corresponding chemical structures of the materials used. Reproduced with permission from Vasilopoulou, M. Georgiadou, D. G. etal. Microelectron. Eng. 2009,86(4-6), 1511-1514. ...

This section covers early indirect fiber optic chemical sensors (FOCS) for species that cannot be sensed directly but require the use of indicators, probes, labeled biomolecules, or color-forming reactions. 

This process involves the suspension of the biocatalyst in a monomer solution which is polymerized, and the enzymes are entrapped within the polymer lattice during the crosslinking process. This method differs from the covalent binding that the enzyme itself does not bind to the gel matrix. Due to the size of the biomolecule it will not diffuse out of the polymer network but small substrate or product molecules can transfer across or within it to ensure the continuous transformation. For sensing purposes, the polymer matrix can be formed directly on the surface of the fiber, or polymerized onto a transparent support (for instance, glass) that is then coupled to the fiber. The most popular matrices include polyacrylamide (Figure 5), silicone rubber, poly(vinyl alcohol), starch and polyurethane. 

Conventional evanescent sensing works exceedingly well for relatively small biomolecules such as proteins and DNA molecules whose size is much smaller than the decay length. However, it becomes less sensitive when detecting biospecies, such as cells, with dimensions over 1 pm. In Chap. 15, deep-probe waveguide sensors are developed to overcome this limitation, which have a decay length comparable to the size of the biospecies of interest. 

In surface sensing, the adsorbed biomolecules onto the inner wall of a microtube will change the wave vector of a supported mode from A 0 to k and the electric field from E0 to ). These unperturbed (L0) and perturbed (E ) electric fields still satisfied wave equation ... 

The biomolecule sensitivity is defined as the magnitude of the resonant mode shift for a given biomolecule surface density, i.e. fi/L/ap. Upon determining the biomolecule sensitivity, the detection limit (DL) can be calculated. The DL is the minimum surface density of biomolecules that can possibly be measured by the sensing device ... 

It is often desirable to immobilize different biomolecules on different sensing elements in close proximity on the same nanophotonic sensor in the development of a multiplexed sensor. This is the case in the example of parallel ID photonic crystal resonators described in Sect. 16.4. Cross-contamination of biomolecules must be avoided in order to preserve high specificity. We have found that a combination of parylene biopatteming and polydimethylsiloxane (PDMS) microfluidics is a convenient means to immobilized multiple biomolecules in close proximity without cross-contamination as shown in Fig. 16.8. Parylene biopatteming is first used to expose only the regions of highest optical intensity of the nanosensor for functionalization. Second, a set of PDMS microfluidics is applied to the parylene-pattemed nanophotonic sensor, and the biomolecules to be attached... 

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