Use of a geometry optimized fiber-optic surface-enhanced Raman scattering sensor in trace detection

Lab-on-Fiber Sensors with Ag/Au Nanocap Arrays Based on the Two Deposits of Polystyrene Nanospheres

Surface-enhanced Raman spectroscopy (SERS) can boost the pristine Raman signal significantly which could be exploited for producing innovative sensing devices with advanced properties. However, the inherent complexity of SERS systems restricts their further applications in rapid detection, especially in situ detection in narrow areas. Here, we construct an efficient and flexible SERS-based Lab-on-Fiber (LOF) sensor by integrating Ag/Au nanocap arrays obtained by Ag/Au coating polystyrene nanospheres on the optical fiber face. We obtain rich "hot spots" at the nanogaps between neighboring nanocaps, and further achieve SERS performance with the assistance of laser-induced thermophoresis on the metal film that can achieve efficiency aggregation of detected molecules. We achieve a high Raman enhancement with a low detection limitation of 10-7 mol/L for the most efficient samples based on the above sensor. This sensor also exhibits good repeatability and stability under multiple detections, revealing the potential application for in situ detection based on the reflexivity of the optical fiber.

A surface-enhanced Raman scattering optrode prepared by in situ photoinduced reactions and its application for highly sensitive on-chip detection

A surface-enhanced Raman scattering (SERS)-active optical fiber sensor combining the optical fiber waveguide with various SERS substrates has been a powerful analytical tool for in situ and long-distance SERS detection with high sensitivity. The design and modification of a high-quality SERS-active sensing layer are important topics in the development of novel SERS-active optical fiber sensors. Here, we prepared a highly sensitive SERS-active optrode by in situ fabrication of a three-dimensional porous structure on the optical fiber end via a photoinduced polymerization reaction, followed by the growth of photochemical silver nanoparticles above the porous polymer material. The fabrication process is rapid (finished within 1 h) and can be on line under light control. The porous structure supports vast silver nanoparticles, which allows for strong electromagnetic enhancement of SERS. Interestingly, the preparation of this SERS optrode and its utilization for SERS detection can all be conducted in a microfluidic chip. The qualitative and quantitative on-chip SERS sensing of organic pollutants and pesticides has been achieved by this SERS optrode-integrated microfluidic chip, and its high detection sensitivity makes it a promising factor in the analysis of liquid systems.

A double-taper optical fiber-based radiation wave other than evanescent wave in all-fiber immunofluorescence biosensor for quantitative detection of Escherichia coli O157:H7

Cylindrical or taper-and-cylinder combination optical fiber probe based on evanescent wave has been widely used for immunofluorescence biosensor to detect various analytes. In this study, in contrast to the contradiction between penetration depth and analyte diameter of optical fiber probe-based evanescent wave, we demonstrate that double-taper optical fiber used in a radiation wave-based all-fiber immunofluorescence biosensor (RWAIB) can detect micron-scale analytes using Escherichia coli O157:H7 as representative target. Finite-difference time-domain method was used to compare the properties of evanescent wave and radiation wave (RW). Ray-tracing model was formulated to optimize the taper geometry of the probe. Based on a commercial multi-mode fiber, a double-taper probe was fabricated and connected with biosensor through a "ferrule connector" optical fiber connector. The RWAIB configuration was accomplished using commercial multi-mode fibers and fiber-based devices according to the "all-fiber" method. The standard sample tests revealed that the sensitivity of the proposed technique for E. coli O157:H7 detection was 10(3) cfu · mL(-1). Quantitation could be achieved within the concentration range of 10(3) cfu · mL(-1) to 107 cfu · mL(-1). No non-specific recognition to ten kinds of food-borne pathogens was observed. The results demonstrated that based on the double-taper optical fiber RWAIB can be used for the quantitative detection of micron-scale targets, and RW sensing is an alternative for traditional evanescent wave sensing during the fabrication of fiber-optic biosensors.

Surface-enhanced Raman scattering (SERS) optrodes for multiplexed on-chip sensing of nile blue A and oxazine 720

The fabrication and on-chip integration of surface-enhanced Raman scattering (SERS) optrodes are presented. In the optrode configuration, both the laser excitation and the back-scattered Raman signal are transmitted through the same optical fiber. The SERS-active component of the optrode was fabricated through the self-assembly of silver nanoparticles on the tip of optical fibers. The application of SERS optrodes to detect dyes in aqueous solution indicated a limit of quantification below 1 nM, using nile blue A as a molecular probe. Using the optrode-integrated microfluidic chip, it was possible to detect several different dyes from solutions sequentially injected into the same channel. This approach for sequential detection of different analytes is applicable to monitoring on-chip chemical processes. The narrow bandwidth of the vibrational information generated by SERS allowed solutions of different compositions of two chemically similar dyes to be distinguished using a dilution microfluidic chip. These results demonstrate the advantages of the SERS-optrode for microfluidics applications by illustrating the potential of this vibrational method to quantify components in a mixture.

A review on the fabrication of substrates for surface enhanced Raman spectroscopy and their applications in analytical chemistry

This work reviews different types of substrates used for surface-enhanced Raman scattering (SERS) that have been developed in the last 10 years. The different techniques of self-assembly to immobilize metallic nanoparticles on solid support are covered. An overview of SERS platforms developed using nanolithography methods, including electron-beam (e-beam) lithography and focused ion beam (FIB) milling are also included, together with several examples of template-based methodologies to generate metallic nano-patterns. The potential of SERS to impact several aspects of analytical chemistry is demonstrated by selected examples of applications in electrochemistry, biosensing, environmental analysis, and remote sensing. This review shows that highly enhancing SERS substrates with a high degree of reliability and reproducibility can now be fabricated at relative low cost, indicating that SERS may finally realize its full potential as a very sensitive tool for routine analytical applications.

Resonance Rayleigh scattering spectra, non-linear scattering spectra of malachite green-12-tungstophosphoric acid system and its analytical application in fish

In 0.1 molL(-1) (pH 1.0) HCl medium, 12-tungstophosphoric acid (TP) reacted with malachite green (MG) to form an ion-association complex. As a result, the new spectra of RRS, SOS and FDS appeared and their intensities were enhanced greatly. The maximum wavelengths of RRS, SOS and FDS were located at 334 nm, 586 nm and 330 nm, and the scattering intensities were proportional to the concentration of MG. Based on it a new method for the determination of MG has been established. The detection limits (3σ) of these methods were in the range of 3.7-27 ng mL(-1). The RRS, SOS, and FDS characteristics, absorption spectrum characteristics and optimum reaction conditions of the system were discussed. Effects of coexistent substances were tested, and the results demonstrated that this method had good selectivity. It has been applied to the determination of malachite green residues in fish flesh with satisfactory results. The reaction mechanism and reasons of RRS enhancement are discussed.

Optical fiber LSPR biosensor prepared by gold nanoparticle assembly on polyelectrolyte multilayer

This article provides a novel method of constructing an optical fiber localized surface plasmon resonance (LSPR) biosensor. A gold nanoparticle (NP) assembled film as the sensing layer was built on the polyelectrolyte (PE) multilayer modified sidewall of an unclad optical fiber. By using a trilayer PE structure, we obtained a monodisperse gold NP assembled film. The preparation procedure for this LSPR sensor is simple and time saving. The optical fiber LSPR sensor has higher sensitivity and outstanding reproducibility. The higher anti-interference ability for response to an antibody makes it a promising method in application as a portable immuno-sensor.

Local electric field enhancement and polarization effects in a surface-enhanced Raman scattering fiber sensor with chessboard nanostructure

A surface-enhanced Raman scattering fiber sensor with chessboard nanostructure on a cleaved fiber facet is studied by finite-difference time-domain method. Surface plasmons at the metal coated nanostructured fiber facet can be effectively excited and strong local electric field enhancement is obtained. Studies on the influence of light polarization demonstrate a large polarization dependence of the field enhancement factor while the polarization effects on the plasmon resonance wavelength are relatively small.