Single Plasmon-Active Optical Fiber Probe for Instantaneous Chiral Detection

Abstract

The chiral recognition of organic compounds is of vital importance in the field of pharmacology and medicine. Unfortunately, the common analytical routes used in this field are significantly restricted by time spent and equipment demands. In this work, we propose an unprecedented alternative, aimed at enantiomer discrimination and estimation of their concentrations in an uncomplicated and instantaneous manner. The proposed approach is based on the creation of an optical fiber probe with two pronounced plasmonic bands attributed to gold and silver. The gold or silver surfaces were grafted with moieties, able to enunciating entrap chiral amines from solution, resulting in a wavelength shift corresponding to each plasmonic metal. As a model compound of chiral amine, we chose the DOPA, also taking in mind its high medical relevancy. For chiral detection, the optical fiber probe was simply immersed in an analytical solution of DOPA, and the selective shift of gold or silver plasmon bands was observed in the reflected light depending on DOPA chirality. The observed shifts depend on the concentration of DOPA enantiomers. In the case of a racemic mixture, the shifts of both plasmonic bands emerge, making possible the simultaneous determination of enantiomer concentrations and their ratio. The analytical cycle takes several minutes and requires very simple laboratory equipment.

Enhanced sensitivity of fiber SPR sensor by metal nanoparticle

“…The 12 nm gold nanosphere is chosen to enhance the sensitivity, the sensitivity reaches 5,140 nm/RIU. In Miliutina et al (2019a, 2019b, 2019c), a similar method was used to realize immobilization of gold nanoparticles with sharp edges on the thin gold layer, deposited on the multimode fiber surface for improvement of the sensor functionality. After a rough calculation, the average sensitivity was 3,384 nm/RIU which is lower than the highest sensitivity in this paper.…”

“…So, fiber SPR sensor has been widely used in biochemical detection, medical sample monitoring, environment and food detection in recent years (Wolfbeis, 2004; Shi et al , 2014; Chen et al , 2016; Weng et al , 2016; Gong et al , 2019). Besides, the metal-coated SPR fiber sensor functioned with all kinds of functional groups is used to realize the detection of the particular substance (Miliutina et al , 2019a, 2019b, 2019c, 2020). The traditional fiber SPR sensor is based on multimode fiber structure (Jorgenson and Yee, 1993, 1994; Ronot-Trioli et al , 1996; Tsai et al , 2005; Lin et al , 2008; Huang et al , 2013), which makes the sensitivity of fiber-based SPR sensors lower than that of prism-based SPR sensors because of the multi-mode transmission.…”

“…Based on that, Niu et al (2019) placed gold nanoparticles on the gold film to realize the sensitivity enhancement of the D-type large-core fiber SPR sensor. Miliutina et al (2019a, 2019b, 2019b) used the metal-coated multimode fiber functionalized with the nanoparticles to realize the refractive index detection. However, the large-core fiber and multimode fiber have multi-mode transmission, which will impact the sensitivity of the sensor.…”

Conceptual Developments of Aryldiazonium Salts as Modifiers for Gold Colloids and Surfaces

“…18,[42][43][44] The group of Postnikov and Lyutakov developed methods of diazonium modification for the fabrication of 2D SERS and optical fiber-based surface plasmon resonance (SPR) sensors. [45][46][47] Their comprehensive investigation on the functionalization of thin gold films of 18 nm using stable aryldiazonium tosylates studied the spontaneous and electrochemical modification in water with -NO 2 , -NH 2 , -COOH, and -C 8 F 17 substituents (Figure 4A). 48 It was concluded that depending on the substituent and activation method, diazonium salts can graft 1-10 phenylene layers.…”

“…Diazonium modification of flat gold surfaces via an electrochemical reduction route began with the attachment of phenylene functional groups to gold wires and electrodes. However, recently the focus has shifted to the functionalization of nanometer-scale gold films, which provide unique electrical and optical properties. ,− The group of Postnikov and Lyutakov developed methods of diazonium modification for the fabrication of 2D SERS and optical fiber-based surface plasmon resonance (SPR) sensors. − Their comprehensive investigation of the functionalization of thin gold films of 18–20 nm using stable aryldiazonium tosylates studied the spontaneous and electrochemical modification in water with −NO 2 , −NH 2 , −COOH, and −C 8 F 17 substituents . It was concluded that depending on the substituent and activation method, diazonium salts can yield a polyaryl layer of up to 10 aryl repeat units.…”