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Surface plasmon resonance (SPR) based sensors play an important role in the biological and medical fields, and improving the sensitivity is a goal that has always been pursued. In this paper, a sensitivity enhancement scheme jointly employing MoS2 nanoflower (MNF) and nanodiamond (ND) to co-engineer the plasmonic surface was proposed and demonstrated. The scheme could be easily implemented via physically depositing MNF and ND overlayers on the gold surface of an SPR chip, and the overlayer could be flexibly adjusted by controlling the deposition times, thus approaching the optimal performance. The bulk RI sensitivity was enhanced from 9682 to 12,219 nm/RIU under the optimal condition that successively deposited MNF and ND 1 and 2 times. The proposed scheme was proved in an IgG immunoassay, where the sensitivity was twice enhanced compared to the traditional bare gold surface. Characterization and simulation results revealed that the improvement arose from the enhanced sensing field and increased antibody loading via the deposited MNF and ND overlayer. At the same time, the versatile surface property of NDs allowed a specifically-functionalized sensor using the standard method compatible with a gold surface. Besides, the application for pseudorabies virus detection in serum solution was also demonstrated. [ABSTRACT FROM AUTHOR]

Biosensors based on surface plasmon resonance (SPR) have shown significant applications in drug screening, environmental monitoring, immunoassay, etc.; however, improving the sensitivity of these biosensors is one of the prime tasks at present. In this study, taking advantage of the special optical and morphological characteristics of MoS2 nanoflowers, we synthesized a sensitivity-improved SPR biosensor by successively depositing MoS2 nanoflowers and gold nanoparticles (AuNPs) on a traditional SPR sensor and then applied this biosensor to the immunoassay of mouse IgG. It was found that the deposition of the MoS2 nanoflowers could improve the bulk refractive index sensitivity from 2212.2 to 2857.2 nm per RIU (RIU: refractive index unit); however, the further addition of AuNPs resulted in a decrease in the bulk refractive index sensitivity to 2149.7 nm per RIU. Moreover, when the proposed biosensor was applied to the IgG immunoassay, a 0.047 nm (μg mL−1)−1 sensitivity of the MoS2–AuNP-modified sensor was achieved, which was ∼3 times that of the unmodified sensor (0.016 nm (μg mL−1)−1). This improvement in the sensitivity of the biosensor towards IgG can be attributed to the flower-like morphology of MoS2 that provides more sites for the loading of AuNPs, thus facilitating the immobilization of a larger amount of IgG antibody on the surface of the sensor. Because of its simple fabrication process and compatibility with the standard bio-activation method of gold surface, the proposed biosensor provides an easily-accessible platform for biological analysis and detection with improved sensitivity. [ABSTRACT FROM AUTHOR]

The longitudinal relaxation time (termed as T 1 ) of nitrogen-vacancy (NV) centers in nanodiamonds can be affected by surface electric or magnetic noise, which has been exploited to develop cutting-edge quantum relaxometry for biochemical sensing. In this work, a tiny all-fiber quantum probe based on longitudinal relaxometry was developed by chemically-anchoring nanodiamonds on the surface of a cone fiber tip. The dependences of T 1 on surface electric and magnetic noise were discussed in theories first and then experimentally demonstrated in varied pH and Gd 3+ concentration solutions, respectively. Because of NV centers being subject to enhanced coupling from surface noise, T 1 reduced from 290 to 245 µs when pH changed from 3 to 9 and reduced to 220 µs when Gd 3+ concentration increased to 10 mM, agreeing well with theoretical results. Based on these, the Gd 3+ -tagged-biotin and streptavidin model was designed and implemented on the all-fiber probe, and results demonstrated the detection of biotin with a limit of 168 nM and good specificity. This paper opens a new way to develop an all-fiber quantum probe by exploiting the unique electrical spin properties of NV centers, and the probe shows great potential for biological detection with high sensitivity and specificity.