Mid-infrared surface sensing based ontTwo-dimensional materials

(English) Mid-infrared (mid-IR) spectroscopy in the wavelength region between 2 and 20 µm is a powerful technique to identify vibrational absorption signatures of molecules, finding in this way extensive applications in healthcare, environmental monitoring, and chemical analysis. Enhanced IR light-molecules interactions can be achieved by exploiting nanostructured surfaces supporting polaritons – hybrid excitations of light and dipolar elements of matter. Recently, polaritons of two-dimensional van der Waals (2D-vdW) materials unveiled a vibrant playground for mid-IR spectroscopy as they possess remarkable properties such as light trapping at deep nanoscale. This dissertation aims to investigate 2D-vdW materials for technological sensing applications. Hence, we explore the mid-IR sensing performance of nanostructures of widely studied 2D-vdW crystals: graphene (the pioneering vdW material with tunable plasmon polaritons) and hexagonal boron nitride (hBN, sustaining ultralow-loss phonon polaritons). Relevant functionalization layers, such as polymer adsorber and antibodies, are combined with the 2D-vdW nanostructures to create gas and for bio-molecular sensors, respectively. Here, we present three main experimental works of 2D-vdW-based mid-IR molecular sensing. First, we investigate the CO2 detection using graphene nanoribbons functionalized with ultrathin CO2-chemisorbing polyethylenimine (PEI). The localized surface plasmon resonance (LSPR) of graphene is modulated by varying CO2 gas concentration, whose substantial shifts are influenced by the reversible PEI-induced doping of graphene. Second, we examine the phonon-enhanced CO2 detection of hBN nanoresonators functionalized with thin PEI layer. The phonon-polariton resonance is modulated by varying CO2 levels with high signal-to-noise ratio signals. Third, we present a quantitative bioassay by transducing different vitamin B12 target concentrations into LSPR shifts of bio-functionalized graphene nanostructures (subsequent addition of pyrene linkers and recombinant anti-vB12 antibody fragments). Additionally, we observed the same result-trends for the same bioassay using graphene nanostructures fabricated both by small-scale (i.e., electron beam lithography) and large-scale (i.e., nanoimprint lithography) methods. Our proof-of-concept mid-IR sensing experiments show quantitative results for the detection of gas and biomarker with functionalized 2D-vdW nanostructures. The opportunity of combining the mid-IR spectroscopy with industrially large-scale 2D-vdW nanostructures (e.g., nanoimprinted GNH in this dissertation) would enable cost-effective technologies in future developments. This dissertation contributes to the field of 2D-vdW-based mid-IR spectroscopic sensors towards exploring novel designs and improved sensitivity, which eventually could lower the limit of detection for molecular analytes in various applications.(Español) La espectroscopia infrarroja de onda media (mid-IR en inglés) en el rango óptico entre 2 y 20 µm es una potente técnica para identificar las huellas vibracionales de las moléculas, permitiendo así su uso en múltiples aplicaciones como salud, monitoreo medioambiental y análisis químico. Aumentar las interacciones luz-molécula en el IR es posible explotando superficies nano-estructuradas que soportan polaritones – excitaciones hibridas entre la luz y dipolos en la materia. Recientemente, polaritones en materiales bidimensionales de van der Waals (2D-vdW) han revelado un escenario interesante para la espectroscopia en el mid-IR, ya que poseen propiedades remarcables como la de confinar la luz a escala nanométrica. Esta tesis pretende investigar materiales 2D-vdW para su uso tecnológico en aplicaciones de detección. De esta manera, exploramos el rendimiento de la detección en el mid-IR de nanoestructuras de cristales 2D-vdW ampliamente estudiados: grafeno (el material vdW pionero con plasmones-polaritones sintonizables) y el nitruro de boro hexagonal (hBN, que soporta fonones-polaritones con muy bajas perdidas). Capas adicionales para la funcionalización, como polímeros absorbentes y anticuerpos, son combinadas con las nanoestructuras 2D-vdW para crear sensores de gas y biomoleculares, respectivamente. Aquí presentamos tres principales trabajos experimentales para la detección de moléculas con materiales 2D-vdW en el mid-IR. Primero, investigamos la detección de CO2 usando nanoribons de grafeno funcionalizado con una capa ultrafina de polietilenimina (PEI), dada su quimisorción de CO2. La resonancia de plasmón de superficie localizada (LSPR) del grafeno es modulada variando la concentración del CO2, cuyos desplazamientos dependen de un efecto de dopaje quimico reversible inducido por el PEI. Después, examinamos la detección realzada de CO2 con fonones a partir de nanoresonadores de hBN funcionalizados con una capa fina de PEI. La resonancia fonón-polaritón es modulada variando los niveles de CO2 con una gran relación señal/ruido. Finalmente, presentamos un bioensayo cuantitativo a partir de la transducción de distintas concentraciones de vitamina B12 a desplazamientos de LSPR con nanoestructuras bio-funcionalizadas de grafeno (con la posterior adición de enlazadores de pireno y anticuerpos fragmentos de recombinante anti-vB12) Adicionalmente, observamos la misma tendencia de resultados para el mismo bioensayo usando nanoestructuras de grafeno fabricadas con métodos no escalables (i.e., litografía por haz de electrones) y escalable (i.e., litografía por nanoimpresión). Nuestras pruebas de concepto con experimentos de detección con luz mid-IR muestran resultados cuantitativos para la detección de gas y biomarcadores con nanoestructuras 2D-vdW funcionalizadas. La oportunidad de poder combinar la espectroscopia mid-IR con nanoestructuras de materiales 2D-vdW industrialmente escalables (ej., GNH via nanoimpresión en esta tesis) podrían permitir desarrollar tecnologías rentables en el futuro. Esta tesis pretende contribuir en el campo de los sensores para espectroscopia mid-IR basados en materiales 2D-vdW, explorando novedosos diseños y mejorando su sensibilidad, los cuales podrían eventualmente reducir el límite de detección para analitos moleculares en varias aplicaciones.Fotònic

Mid-infrared surface sensing based ontTwo-dimensional materials

(English) Mid-infrared (mid-IR) spectroscopy in the wavelength region between 2 and 20 µm is a powerful technique to identify vibrational absorption signatures of molecules, finding in this way extensive applications in healthcare, environmental monitoring, and chemical analysis. Enhanced IR light-molecules interactions can be achieved by exploiting nanostructured surfaces supporting polaritons – hybrid excitations of light and dipolar elements of matter. Recently, polaritons of two-dimensional van der Waals (2D-vdW) materials unveiled a vibrant playground for mid-IR spectroscopy as they possess remarkable properties such as light trapping at deep nanoscale. This dissertation aims to investigate 2D-vdW materials for technological sensing applications. Hence, we explore the mid-IR sensing performance of nanostructures of widely studied 2D-vdW crystals: graphene (the pioneering vdW material with tunable plasmon polaritons) and hexagonal boron nitride (hBN, sustaining ultralow-loss phonon polaritons). Relevant functionalization layers, such as polymer adsorber and antibodies, are combined with the 2D-vdW nanostructures to create gas and for bio-molecular sensors, respectively. Here, we present three main experimental works of 2D-vdW-based mid-IR molecular sensing. First, we investigate the CO2 detection using graphene nanoribbons functionalized with ultrathin CO2-chemisorbing polyethylenimine (PEI). The localized surface plasmon resonance (LSPR) of graphene is modulated by varying CO2 gas concentration, whose substantial shifts are influenced by the reversible PEI-induced doping of graphene. Second, we examine the phonon-enhanced CO2 detection of hBN nanoresonators functionalized with thin PEI layer. The phonon-polariton resonance is modulated by varying CO2 levels with high signal-to-noise ratio signals. Third, we present a quantitative bioassay by transducing different vitamin B12 target concentrations into LSPR shifts of bio-functionalized graphene nanostructures (subsequent addition of pyrene linkers and recombinant anti-vB12 antibody fragments). Additionally, we observed the same result-trends for the same bioassay using graphene nanostructures fabricated both by small-scale (i.e., electron beam lithography) and large-scale (i.e., nanoimprint lithography) methods. Our proof-of-concept mid-IR sensing experiments show quantitative results for the detection of gas and biomarker with functionalized 2D-vdW nanostructures. The opportunity of combining the mid-IR spectroscopy with industrially large-scale 2D-vdW nanostructures (e.g., nanoimprinted GNH in this dissertation) would enable cost-effective technologies in future developments. This dissertation contributes to the field of 2D-vdW-based mid-IR spectroscopic sensors towards exploring novel designs and improved sensitivity, which eventually could lower the limit of detection for molecular analytes in various applications.(Español) La espectroscopia infrarroja de onda media (mid-IR en inglés) en el rango óptico entre 2 y 20 µm es una potente técnica para identificar las huellas vibracionales de las moléculas, permitiendo así su uso en múltiples aplicaciones como salud, monitoreo medioambiental y análisis químico. Aumentar las interacciones luz-molécula en el IR es posible explotando superficies nano-estructuradas que soportan polaritones – excitaciones hibridas entre la luz y dipolos en la materia. Recientemente, polaritones en materiales bidimensionales de van der Waals (2D-vdW) han revelado un escenario interesante para la espectroscopia en el mid-IR, ya que poseen propiedades remarcables como la de confinar la luz a escala nanométrica. Esta tesis pretende investigar materiales 2D-vdW para su uso tecnológico en aplicaciones de detección. De esta manera, exploramos el rendimiento de la detección en el mid-IR de nanoestructuras de cristales 2D-vdW ampliamente estudiados: grafeno (el material vdW pionero con plasmones-polaritones sintonizables) y el nitruro de boro hexagonal (hBN, que soporta fonones-polaritones con muy bajas perdidas). Capas adicionales para la funcionalización, como polímeros absorbentes y anticuerpos, son combinadas con las nanoestructuras 2D-vdW para crear sensores de gas y biomoleculares, respectivamente. Aquí presentamos tres principales trabajos experimentales para la detección de moléculas con materiales 2D-vdW en el mid-IR. Primero, investigamos la detección de CO2 usando nanoribons de grafeno funcionalizado con una capa ultrafina de polietilenimina (PEI), dada su quimisorción de CO2. La resonancia de plasmón de superficie localizada (LSPR) del grafeno es modulada variando la concentración del CO2, cuyos desplazamientos dependen de un efecto de dopaje quimico reversible inducido por el PEI. Después, examinamos la detección realzada de CO2 con fonones a partir de nanoresonadores de hBN funcionalizados con una capa fina de PEI. La resonancia fonón-polaritón es modulada variando los niveles de CO2 con una gran relación señal/ruido. Finalmente, presentamos un bioensayo cuantitativo a partir de la transducción de distintas concentraciones de vitamina B12 a desplazamientos de LSPR con nanoestructuras bio-funcionalizadas de grafeno (con la posterior adición de enlazadores de pireno y anticuerpos fragmentos de recombinante anti-vB12) Adicionalmente, observamos la misma tendencia de resultados para el mismo bioensayo usando nanoestructuras de grafeno fabricadas con métodos no escalables (i.e., litografía por haz de electrones) y escalable (i.e., litografía por nanoimpresión). Nuestras pruebas de concepto con experimentos de detección con luz mid-IR muestran resultados cuantitativos para la detección de gas y biomarcadores con nanoestructuras 2D-vdW funcionalizadas. La oportunidad de poder combinar la espectroscopia mid-IR con nanoestructuras de materiales 2D-vdW industrialmente escalables (ej., GNH via nanoimpresión en esta tesis) podrían permitir desarrollar tecnologías rentables en el futuro. Esta tesis pretende contribuir en el campo de los sensores para espectroscopia mid-IR basados en materiales 2D-vdW, explorando novedosos diseños y mejorando su sensibilidad, los cuales podrían eventualmente reducir el límite de detección para analitos moleculares en varias aplicaciones.Postprint (published version

Mid-infrared Gas Sensing Using Graphene Plasmons Tuned by Reversible Chemical Doping

Highly confined plasmon modes in nanostructured graphene can be used to detect tiny quantities of biological and gas molecules. In biosensing, a specific biomarker can be concentrated close to graphene, where the optical field is enhanced, by using an ad-hoc functional layer (e.g., antibodies). Inspired by this approach, in this paper we exploit the chemical and gas adsorption properties of an ultrathin polymer layer deposited on a nanostructured graphene surface to demonstrate a new gas sensing scheme. A proof-of-concept experiment using polyethylenimine (PEI) that is chemically reactive to CO2 molecules is presented. Upon CO2 adsorption, the sensor optical response changes because of PEI vibrational modes enhancement and shift in plasmon resonance, the latter related to polymer-induced doping of graphene. We show that the change in optical response is reversed during CO2 desorption. The demonstrated limit of detection (LOD) of 390 ppm corresponds to the lowest value detectable in ambient atmosphere, which can be lowered by operating in vacuum. By using specific adsorption polymers, the proposed sensing scheme can be easily extended to other relevant gases, for example, volatile organic compounds.Peer ReviewedPostprint (published version

Phonon-enhanced mid-infrared CO2 gas sensing using boron nitride nanoresonators

Hexagonal boron nitride (hBN) hosts long-lived phonon polaritons, yielding a strong mid-infrared (mid-IR) electric field enhancement and concentration on the nanometer scale. It is thus a promising material for highly sensitive mid-IR sensing and spectroscopy. In addition, hBN possesses high chemical and thermal stability as well as mechanical durability, making it suitable for operation in demanding environments. In this work, we demonstrate a mid-IR CO2 gas sensor exploiting phonon polariton (PhP) modes in hBN nanoresonators functionalized by a thin CO2-adsorbing polyethylenimine (PEI) layer. We find that the PhP resonance shifts to lower frequency, weakens, and broadens for increasing CO2 concentrations, which are related to the change of the permittivity of PEI upon CO2 adsorption. Moreover, the PhP resonance exhibits a high signal-to-noise ratio even for small ribbon arrays of 30 × 30 μm2. Our results show the potential of hBN nanoresonators to become a novel platform for miniaturized phonon-enhanced SEIRA gas sensors.The research leading to these results has received funding from the H2020 Programme under Grant Agreement No. 881603 (Graphene Flagship). This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 754510. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 665884. This work was partially funded by CEX2019-000910-S [MICINN/AEI/10.13039/501100011033] and Project TUNA-SURF (PID2019-106892RB-I00), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya through CERCA. We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities (RTI2018-094830-B-100 and the Project MDM-2016-0618 of the Maria de Maeztu Units of Excellence Program) and the Basque Government (Grant Number IT1164-19). We acknowledge the Ministry of Science, Innovation and Universities through the ‘Maria de Maezt’ Programme for Units of Excellence in R&D (CEX2018-000805-M). Further, support from the Materials Engineering and Processing program of the National Science Foundation, Award Number CMMI 1538127 for h-BN crystal growth is greatly appreciated. The hBN crystals growth is also supported by an Office of Naval Research Award No. N00014-20-1-2474. I.D. acknowledges the Basque Government (Grant No. PRE_2019_2_0164). We acknowledge Project PID2020-115221GB-C41 financed by MCIN/AEI/10.13039/501100011033 and Aragon Government through Project Q-MAD.Peer reviewe

Controlling mid-infrared plasmons in graphene nanostructures through post-fabrication chemical doping

Engineering the doping level in graphene nanostructures to yield controlled and intense localized surface plasmon resonance (LSPR) is fundamental for their practical use in applications such as molecular sensing for point of care or environmental monitoring. In this work, we experimentally study how chemical doping of graphene nanostructures using ethylene amines affects their mid-infrared plasmonic response following the induced change in electrical transport properties. Combining post-fabrication silanization and amine doping allows to prepare the surface to support a strong LSPR response at zero bias. These findings pave the way to design highly doped graphene LSPR surfaces for infrared sensors operating in real environments.Peer ReviewedPostprint (published version

Quantitative Mid-Infrared Plasmonic Biosensing on Scalable Graphene Nanostructures

Graphene nanostructures, exhibiting tunable and nanoscale-confined mid-infrared (mid-IR) plasmons, prevail as a powerful spectroscopic platform for novel surface-enhanced molecular identification. Particularly, graphene shows exciting opportunities for biosensing applications due to its versatile functionalization methods with different biomolecular building blocks (e.g., enzymes, proteins, and DNA). Here, a quantitative bioassay based on the mid-IR localized surface plasmon resonance (LSPR) modulation in functionalized graphene nanostructures is demonstrated. Specifically, vitamin B12 (vB12) using the specific recognition elements on modified graphene nanoribbons (i.e., pyrene linkers via π − π stacking + anti-vB12 antibody fragments via amide bond) is detected. Different concentrations of vB12 spotted on an arrayed panel of a single chip are quantified by the graphene LSPR shifts, where a limit of detection (LOD) of 53.5 ng mL−1 is obtained. The upscaling potential of the bioassay using large area nanostructured graphene films produced by nanoimprinting 2D hole arrays is illustrated. The integration of quantitative bioassay with scalable graphene nanostructures shows promising routes of graphene-based mid-IR platforms toward prospective industrial applications.N.B. and E.W. contributed equally to this work. Tuula Kuurila and Salla Pentikäinen from VTT were thanked for technical assistance in antibody production and purification. Harri Siitari was thanked for support as a project manager during the anti-vB12 antibody development. The authors thank Daniel Martinez for help with AFM measurements. The research leading to these results has received funding from the H2020 Programme under Grant Agreement No. 881603 (Graphene Flagship). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 754510. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 665884. The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (CEX2019-000910-S and CEX2019-000917-S) and project TUNA-SURF (PID2019-106892RB-I00) and PID2019-106860GB-I00 (HIGHN), Fundació Mir-Puig, and from Generalitat de Catalunya through the CERCA program, from AGAUR 2017 SGR 1634 and the Beatriu de Pinos-3 Postdoctoral Programme (BP3) under grant agreement ID 801370. This work was partially funded by CEX2019-000910-S [MCIN/ AEI/10.13039/501100011033], Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya through CERCA. Antibody discovery was funded by VTT Technical Research Centre of Finland and Development6 -project funded by Turku Science Park Oy, City of Turku, Turku Bio Valley Ltd.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe