Fabrication of Infrared-Compatible Nanofluidic Devices for Plasmon-Enhanced Infrared Absorption Spectroscopy

Thu Hac Huong Le,Takumi Matsushita,Ryoichi Ohta,Takehiko Kitamori,Yuta Shimoda,Hiroaki Matsui

doi:10.3390/mi11121062

Thu Hac Huong Le, Takumi Matsushita + Show 4 more

Open Access

https://doi.org/10.3390/mi11121062

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Abstract

Nanofluidic devices have offered us fascinating analytical platforms for chemical and bioanalysis by exploiting unique properties of liquids and molecules confined in nanospaces. The increasing interests in nanofluidic analytical devices have triggered the development of new robust and sensitive detection techniques, especially label-free ones. IR absorption spectroscopy is one of the most powerful biochemical analysis methods for identification and quantitative measurement of chemical species in the label-free and non-invasive fashion. However, the low sensitivity and the difficulties in fabrication of IR-compatible nanofluidic devices are major obstacles that restrict the applications of IR spectroscopy in nanofluidics. Here, we realized the bonding of CaF2 and SiO2 at room temperature and demonstrated an IR-compatible nanofluidic device that allowed the IR spectroscopy in a wide range of mid-IR regime. We also performed the integration of metal-insulator-metal perfect absorber metamaterials into nanofluidic devices for plasmon-enhanced infrared absorption spectroscopy with ultrahigh sensitivity. This study also shows a proof-of-concept of the multi-band absorber by combining different types of nanostructures. The results indicate the potential of implementing metamaterials in tracking several characteristic molecular vibrational modes simultaneously, making it possible to identify molecular species in mixture or complex biological entities.

Highlights

As microfluidics and integrated micro chemical systems on-a-chip continue to show great performance and new functionalities in chemical and bioanalysis, synthesis, biosciences and technologies, there is an increasing demand for new robust and sensitive detection techniques
Recent advances in bright mid-IR light sources such as synchrotron radiation or tunable quantum cascade lasers (QCL), as well as mid-IR photon detectors have stimulated the development of highly sensitive Fourier-transformed infrared (FT-IR) spectromicroscopy towards microfluidic applications [8,9,10]. Another approach to overcome the low sensitivity in IR absorption spectroscopy is exploiting the plasmon resonance on a thin film, nanoparticle, or nanostructure of noble metals. This so-called surface enhanced infrared absorption (SEIRA) phenomenon involves the coupling of photon and vibrational modes of molecules when they are located in the enhanced electromagnetic field of a propagating or localized surface plasmon polariton
The emergence of metamaterials—the field of artificial materials composed of metallo-dielectric periodic nanostructures—has offered a new degree of freedom to engineer hot-spots to further improve the performance of SEIRA [13,14]

Summary

Introduction

As microfluidics and integrated micro chemical systems on-a-chip continue to show great performance and new functionalities in chemical and bioanalysis, synthesis, biosciences and technologies, there is an increasing demand for new robust and sensitive detection techniques. The device exhibits a quadrupole plasmon resonant mode, at which the enhanced field is localized in the nanofluidic gap defined by the nanostructures and the mirror film This device allows the introduction of target molecules into the most enhanced electromagnetic field of MIM structures, resulting in a 105-fold improvement in the sensitivity compared to state-of-the-art SEIRA methods employing conventional MIM ones. We demonstrate the integration of MIM structures into the nanochannels and perform a proof-of-concept of plasmon-enhanced infrared absorption spectroscopy in the mid-IR regime below 2000 cm−2, which cannot be achieved by previously reported devices using SiO2 substrates. Ig(uar)e C1.o(na)ceCpotnuceapltudailadgiraagmramoof fmmeettaall--ininsusluatloart-omre-tmale(tMaIlM(M) pIeMrfe)ctpaebrsfoercbterambseotarmbaetrerimaletamaterial structures for plasmon-enhanced infrared absorption spectroscopy, (b) profiles of electric field Ez and structurecsufrroerntpdlaesnmsitoynJx-einndhicaantecdedbyinrefdraarrerdowasbesloucripdtaitoinng stpheecfotrrmosactioopnyo,f(tbh)e pqruoadfirluepsoolef reelseocntarniccefield Ez and current dmenodsiet,yanJxd itnhde itcraatpepdinbgyofrendeaarr-frioelwd seneelrugcyidwaitthiningtthheenfaonromgaapt,ioanndo(fct)hceonqcuepatduraul pdioalgerarmesoofnance mode, and the tnraanpopfliunidgicodfenviecaerin-fiteeglrdateednwerigthyMwIMithpienrfetchteabnsoarnboergsatpru,catunrdes.(c) conceptual diagram of nanofluidic device integrated with MIM perfect absorber structures. Aefmterirlirfto-orffp, iattgteenrenraitsed2a00miμrrmor, which is smaller thalanyetrhiantsiodfe tthheennanaoncohcahnnaenl.nItesl,hoaunldd bthe enoatecdcuthraatctyheidnepsigonseitdiownidathliogfnthmeemnitrruorsipnagttetrhneism20a0skless UV lithographμmymaes,qkwluehsiipschUmViselnsimtthaaolgllelrorawpthhasyntehtqheuaitpfoamfbetrhnietcaanlatlionowoncshtoahnfenmfealbi,rrarincoadrtitolhaneyoaefcrcmusirrianrcoysriildnaeypeotrhssieitnionsniadanelitoghcnehmnaaennnotncuehslaisnn.gnethlse

Fabrication of Nanostructures on Top of the CaF2 Substrate

Bonding of the Device

IR Reflectance Measurement

Numerical Calculation

Fluidic Operation

Leakage Test