Shi et al. [22] confirmed that this kind of HRP-GNP biosensor exhibited long-term stability and good reproducibility.GNPs/CNTs multilayers can also provide a suitable microenvironment to retain enzyme activity and amplify the electrochemical signal of the product of the enzymatic reaction [23]. For example, GNPs/CNTs nanohybrids were covered on the surface of a GCE, which formed an effective antibody immobilization matrix and gave the immobilized biomolecules high stability and bioactivity. The approach provided a linear response range between 0.125 and 80 ng/mL with a detection limit of 40 pg/mL. As shown in Figure 3, because of the advantages of GNPs and CNTs, the hybrid composite has more potential applications for electrochemical sensor, which could be easily extended to other protein detection schemes and DNA analysis [24].

For example, Wang et al. [25] described the fabrication of ZrO2/Au nano-composite films through a combination of sol�Cgel procedure and electroless plating, the organophosphate pesticides (Ops) can be strongly adsorped on the ZrO2/Au film electrode surface, which provides an effective quantitative method for OPs analysis.Figure 3.The immunoassay procedure of GNPs/PDCNTs modified immunosensor using HRP�CGNPs�CAb2 conjugates as label [24].The gold nanorods (GNR) modified electrode layer shows a better analytical response than GNPs [26]. GNR based immunosensors have advantages such as simplicity, being label free, low sample volume, reusability and being more suitable for lab-on-chip devices over gold nanoparticles.

GNRs are sensitive to the dielectric constant of the surrounding medium due to surface plasmon resonance, therefore a slight change of the local refractive index around GNRs will result in an observable plasmon resonance frequency shift. Irudayaraj and Yu fabricated different aspect ratios of GNRs with targeted antibodies to detect three targets (goat anti-human IgG
The wetting properties (and droplet formation) of solutions on surfaces have long been an area of interest [1,2]. Currently, these characteristics are under study due to their importance in several technologies, including composites, printing, coatings, and oil recovery [3,4]. Liquid and colloidal solutions exhibit wetting and droplet formations to varying degrees, depending on their composition [1].

Many semisolid, gel-like solutions form droplets with poor wetting properties, and therefore, make limited contact with a surface. These solutions exhibit thixotropic-like characteristics, where the droplets are semisolid AV-951 and gel-like until acted upon by an outside force, such as lateral shearing or shaking, after which they become liquefied [sol phase; 5]. When the force is removed, the semisolid character returns [5]. The thixotropic behavior of suspensions of biomolecules has also been examined [6].