Nanomaterials for biosensing applications: a review

Abstract

A biosensor device is defined by its biological, or bioinspired receptor unit with unique specificities toward corresponding analytes. These analytes are often of biological origin like DNAs of bacteria or viruses, or proteins which are generated from the immune system (antibodies, antigens) of infected or contaminated living organisms. Such analytes can also be simple molecules like glucose or pollutants when a biological receptor unit with particular specificity is available. One of many other challenges in biosensor development is the efficient signal capture of the biological recognition event (transduction). Such transducers translate the interaction of the analyte with the biological element into electrochemical, electrochemiluminescent, magnetic, gravimetric, or optical signals. In order to increase sensitivities and to lower detection limits down to even individual molecules, nanomaterials are promising candidates due to the possibility to immobilize an enhanced quantity of bioreceptor units at reduced volumes and even to act itself as transduction element. Among such nanomaterials, gold nanoparticles, semi-conductor quantum dots, polymer nanoparticles, carbon nanotubes, nanodiamonds, and graphene are intensively studied. Due to the vast evolution of this research field, this review summarizes in a non-exhaustive way the advantages of nanomaterials by focusing on nano-objects which provide further beneficial properties than "just" an enhanced surface area.

Keywords: biosensors; gold nanoparticles; magnetic nanoparticles; nanostructured carbon; quantum dots.

Figure 1

Schematic presentation of the polarization of the electron density at resonant excitation wavelength. At particle sizes smaller than the excitation wavelength, the oscillating electrons (surface plasmons) cannot propagate along the gold surface leading to a polarization of the electron cloud at one side of the particle.

Figure 2

Illustration of the perturbation of propagating surface plasmons on gold surfaces provoked by gold nanoparticles of defined size and distance leading to an additional change of the evanescent field and therefore to an enhanced signal.

Figure 3

Schematic presentation of the reconstitution of apo-GOx with FAD modified gold nanoparticles enabling the transfer of electron released by the electrocatalytic oxidation of glucose. The collected electrons are then directly transferred to the external circuit giving an electrochemical signal.

Figure 4

Illustration of the FRET principle between QDs and gold nanoparticles and the reestablishing of fluorescence after the recognition event. The target DNA can hybridize either with the receptor DNA, the short sequence of the gold nanoparticle label, or with both. These statistical hybridization events have to be considered for the quantification of the analyte.

Figure 5

Principle of the antenna effect of gold nanoparticles enhancing the excitation rates of QDs when positioned at ~30 nm. This transduction principle might be limited to the identification of analyte DNAs composed of around 15 nucleotides.

Figure 6

Scheme of analyte concentration in complex solutions via bioreceptor modified magnetic nanoparticles. After the recognition event, the captured analytes can be isolated by precipitation of the magnetic nanoparticles in an external magnetic field. When this magnetic field is removed, the nanoparticles can be redispersed. Only the analyte labeled nanoparticles are immobilized on surfaces which are modified with a secondary antibody and thus quantified using diagnostic magnetic resonance transduction.

Figure 7

Oriented immobilization of nitrite reductase from Desulfovibrio desulfuricans on CNTs via hydrophobic interactions between the enzyme and the carbon nanotube surface. This naturally occurring adsorption leads to an efficient electron transfer between the enzyme and the conducting surface where the redox center, after catalytic reduction of nitrite ions to ammonia, can directly be regenerated by the electrode.

Figure 8

Principle of the modulation of the Schottky barrier at source and drain electrodes of CNT field effect transistor devices after hybridization of the receptor DNA with the target DNA. Here, the wrapping properties of DNA around nanotubes inhibit the capability of this receptor DNA to hybridize with its counterpart and thus deactivate indirectly the CNT channel which remains unaffected toward the recognition event.

Figure 9

Adsorption and desorption of a fluorescence dye modified receptor DNA on graphene oxide before and after hybridization with the corresponding target DNA. Graphene oxide quenches the fluorescence of the dye when the receptor unit is adsorbed. By hybridization with the analyte DNA, the receptor DNA and therefor the dye is released which leads to the reestablishment of the fluorescence.