Highly Sensitive Detection of Organic Molecules on the Basis of a Poly(N-isopropylacrylamide) Microassembly Formed by Plasmonic Optical Trapping

Abstract

We demonstrate that a poly(N-isopropylacrylamide) (PNIPAM) microassembly, formed by plasmonic optical trapping, can provide the platform for a highly sensitive detection technique for fluorescent and nonfluorescent organic molecules dissolved in aqueous solution. PNIPAM microassemblies can be easily formed by a combination with a photothermal effect and an enhanced optical force. These physical phenomena were obtained through resonant excitation of localized surface plasmon (LSP). Sparsely distributed fluorescent or nonfluorescent molecules dissolved in solution can be extracted into the PNIPAM assembly, resulting in an increase in fluorescence or Raman signals. In particular, we successfully detected quite small amounts of analytes (rhodamine B) at the 10 mol/L level. Using LSP is an alternative approach in analytical chemistry and can be used in addition to surface enhanced Raman scattering and surface enhanced fluorescence.

Plasmonic Manipulation of DNA using a Combination of Optical and Thermophoretic Forces: Separation of Different-Sized DNA from Mixture Solution

“…Details of our plasmonic optical trapping system combined with fluorescence microspectroscopy have been described elsewhere and in the Supporting Information (Fig. S1) 33,34,55 , and are briefly introduced here. We used a cw near-infrared (NIR) laser (λ = 808 nm) for LSP excitation and cw near-ultraviolet and visible lasers (λ = 375, 473 nm) for fluorescence excitation.…”

“…Following early demonstrations, POT has undergone rapid growth, and has been used to trap various nanomaterials such as polymer beads 10,[19][20][21][22][23][24][25][26][27] , metallic nanoparticles 12,18 , quantum dots 13,28,29 , dye aggregates 30,31 , and so on. In addition to these hard nanospheres, we have demonstrated that POT is also applicable to soft materials such as flexible polymer chains homogeneously dissolved in water 32,33 .…”

Nanostructure-assisted optical tweezers for microspectroscopic polymer analysis

“…We successfully obtained the Raman spectrum of a single particle. Figure 3b shows the Raman spectrum in the high-wavenumber region (2800-3800 cm −1 ) corresponding to the CH stretching modes of the PNIPAM main chain [53,54] Poly(ethylene oxide) [55] Poly(N-isopropylacrylamide) and its derivatives [38,40,56,57] Poly(vinyl methyl ether) [39] Polyfluorene [58,59] (2800-3050 cm −1 ) and those of the OH stretching modes (3100-3800 cm −1 ). With increasing near-infrared laser power, the Raman scattering intensity of the CH stretching modes increased because of the increasing PNIPAM concentration in the microparticle.…”

“…We have demonstrated plasmonic optical tweezers for nanoparticles such as quantum dots [66], polystyrene nanospheres [67,68], J-/H-aggregates [69], DNA [70,71], and polymer chains [72]. Furthermore, we applied POT of PNIPAM for molecular condensation and microspectroscopic detection, as described in the next section [40]. In comparison with conventional optical tweezers, POT has three advantages ( Fig.…”

“…By using this technique, we have performed Raman microspectroscopic analysis on an optically trapped thermoresponsive polymer-rich microdroplet [37,38], providing a new way to determine the polymer concentration of the microdroplet [39]. Furthermore, molecular condensation and detection methods using hydrophobic polymer-rich microdroplets were proposed in a previous report [40]. In this review, we describe the optical trapping of soft matter and the analytical applications.…”