Nanoparticle technology plays a key role in providing opportunities and possibilities for the development of new generation of sensing tools. The targeted sensing of selective biomolecules using functionalized gold nanoparticles (Au NPs) has become a major research thrust in the last decade. Au NP-based sensors are expected to change the very foundations of sensing and detecting biomolecules. In this review, we will discuss the use of surface functionalized Au NPs for smart sensor fabrication leading to detection of specific biomolecules and heavy metal ions.

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In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor structure based on silicon nanosheet and two-dimensional transition metal dichalcogenides. This configuration contains six components: SF10 triangular prism, gold thin film, silicon nanosheet, two-dimensional MoS2/MoSe2/WS2/WSe2 (defined as MX2) layers, biomolecular analyte layer and sensing medium. The minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR curve are systematically examined by using Fresnel equations and the transfer matrix method in the visible and near infrared wavelength range (600 nm to 1024 nm). The variation of the minimum reflectivity and the change in resonance angle as the function of the number of MX2 layers are presented respectively. The results show that silicon nanosheet and MX2 layers can be served as effective light absorption medium. Under resonance conditions, the electrons in these additional dielectric layers can be transferred to the surface of gold thin film. All silicon-MX2 enhanced sensing models show much better performance than that of the conventional sensing scheme where pure Au thin film is used, the highest sensitivity can be achieved by employing 600 nm excitation light wavelength with 35 nm gold thin film and 7 nm thickness silicon nanosheet coated with monolayer WS2.

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Atomically thin transition metal dichalcogenide nanomaterials have shown superior optical and electronic properties in the two-dimensional (2D) scale. They are considered as promising alternative materials to graphene. Here, we have precisely engineered a plasmonic sensing substrate with four types of two-dimensional transition metal dichalcogenide nanomaterial to achieve significant phase sensitivity improvement. Phase modulation is currently the most sensitive interrogation method among all the plasmonic detection approaches. The tuning of the substrate thickness in an atomic scale with a step less than 1 nm allows the efficient modulation of phase signals. More importantly, the optical absorption rate for each of these nanomaterials is different and can be tuned by changing the number of 2D layers, where perfect absorption and interrogation of the plasmonic signal can be obtained. Through systematically optimizing the parameters of the transition metal dichalcogenide structured plasmonic substrate, we can balance the optical absorption efficiencies and the electron losses at the plasmonic resonance condition. All of the calculations were based on the transfer matrix method and Fresnel equations. A very low minimum reflectivity of 3.2560 × 10 −8 was demonstrated with an excitation wavelength of 1024 nm, showing a complete transfer (∼100%) of the light energy into the plasmon resonance energy. The ultradark singularity at the resonance dip leads to an ultrahigh plasmonic sensitivity of 1.1 × 10 7 deg/RIU, which is 3 orders of magnitude higher than those with bare metallic sensing substrates used in commercial plasmonic sensors. The resolution is also improved by at least 3 orders of magnitude compared with conventional substrates.