Nonfluorescent Molecule Detection in 10² nm Nanofluidic Channels by Photothermal Optical Diffraction

Abstract

Integrating analytical systems in 101–103 nm spaces provides ultrasensitive analytical devices at the single cell and the single molecule levels due to the ultrasmall space, and fundamental technologies for nanofluidics are developed. A simple and ultrasensitive detection method is one of the essential technologies for nanofluidics; however, it is still challenging due to the ultrasmall volume at the attoliter to femtoliter scale. In this study, we report a new photothermal detection method of nonfluorescent molecules for a 102 nm space, photothermal optical diffraction (POD), which utilizes light absorption and heat generation by an analyte and optical diffraction by a nanochannel after heat diffusion. Concentration determination of nonfluorescent molecules in a 400 nm channel was successfully demonstrated, and a limit of detection (LOD) of 5.0 μM was achieved, corresponding to 500 molecules (0.84 zmol) in a detection volume of 230 aL. Also, detection in a 200 nm channel was successfully demonstrated without degradation of the LOD. Our method can be widely used for chemical and biological analyses in 102–103 nm nanofluidics.

Detection and Characterization of Individual Nanoparticles in a Liquid by Photothermal Optical Diffraction and Nanofluidics

“…The experimental setup of counting-mode POD is shown in the Supporting Information, (Figure S1). Details such as focal points of lasers, the diffraction pattern, and the detection point are almost the same as those previously reported . The time constant of the lock-in amplifier was set to 2 ms.…”

“…Recently, we developed a photothermal detection method of nonfluorescent molecules in a 10 2 nm channel: photothermal optical diffraction (POD) . Our method realizes the concentration determination of nonfluorescent molecules in a 400 nm channel with a limit of detection of 500 molecules (0.84 zmol).…”

Review of ultrasensitive readout for micro-/nanofluidic devices by thermal lens microscopy

“…68 However, as the fluidic channel is down to a submicron thickness, which is comparable to the wavelength of light, the TLM signal level is reduced due to the short sample length and quicker heat dissipation, and the diffraction theory of the thermal lens effect needs to be revisited. 69,70 Phase-sensitive detections, such as photothermal optical phase shift (POPS) detection, have been exploited to realize background-free detection and to increase the signal-to-background ratio. POPS was first demonstrated as differential interference contrast thermal lens microscopy (DIC-TLM) for the detection of single metallic nanoparticles in microchannels or capillaries, 71,72 and later further developed for the detection of Sunset Yellow FCF, a nonfluorescent dye in the aqueous solution in nanochannels.…”

Advances in Label-Free Detections for Nanofluidic Analytical Devices

“…The enhancement of the POPS signal in 50 nm deep TiO 2 channel was considerably effective, while the POPS signal was not detected in the SiO 2 channel with the same depth. Another approach to the smaller nanochannel using photothermal optical diffraction (POD) was conducted by Tsuyama et al [ 68 ]. In the POD experiment, the probe beam was irradiated to a single nanochannel to observe a diffracted light.…”