Sensing and structure analysis by in situ IR spectroscopy: from mL flow cells to microfluidic applications.

In situ mid-infrared (MIR) spectroscopy in liquids is an emerging field for the analysis of functional surfaces and chemical reactions. Different basic geometries exist for in situ MIR spectroscopy in milliliter (mL) and microfluidic flow cells, such as attenuated total reflection (ATR), simple reflection, transmission and fiber waveguides. After a general introduction of linear optical in situ MIR techniques, the methodology of ATR, ellipsometric and microfluidic applications in single-reflection geometries is presented. Selected examples focusing on thin layers relevant to optical, electronical, polymer, biomedical, sensing and silicon technology are discussed. The development of an optofluidic platform translates IR spectroscopy to the world of micro- and nanofluidics. With the implementation of SEIRA (surface enhanced infrared absorption) interfaces, the sensitivity of optofluidic analyses of biomolecules can be improved significantly. A large variety of enhancement surfaces ranging from tailored nanostructures to metal-island film substrates are promising for this purpose. Meanwhile, time-resolved studies, such as sub-monolayer formation of organic molecules in nL volumes, become available in microscopic or laser-based set-ups. With the adaption of modern brilliant IR sources, such as tunable and broadband IR lasers as well as frequency comb sources, possible applications of far-field IR spectroscopy in in situ sensing with high lateral (sub-mm) and time (sub-s) resolution are considerably extended.

Functionalization of any substrate using covalently modified large area CVD graphene.

We report a novel route for the functionalization of any substrates, including chemically inert substrates. CVD grown graphene is electrochemically functionalized with p-(N-maleimido)phenyl residues and consecutively transferred to various substrates. The transfer process is shown to be without noticeable loss. The functional layer exhibits a thickness of appx. 4.5 nm.

Fabrication and Characterization of Surfaces Modified with Carboxymethylthio Ligands for Chelate-Assisted Trapping of Copper.

The metal ion chelating property was conferred onto silicon (Si) and gold (Au) surfaces by direct electrografting of the 4-[(carboxymethyl)thio]benzenediazonium cation (4-CMTBD). Infrared spectroscopic ellipsometry showed the presence of characteristic phenyl and carbonyl vibrational bands on the functionalized surfaces as a proof of existence of surface-bound organic units of 4-[(carboxymethyl)thio]benzene, (4-CMTB). The loss of diazonium group (N≡N+) upon electrografting of 4-CMTBD was investigated using IR spectroscopy. A Faradaic efficiency of about 18.8-20.0% was realized in mass deposition experiments for grafting 4-CMTB on the Au surface using an electrochemical quartz crystal microbalance technique. Raman spectroscopy performed on the Si-(4-CMTB) surface after treatment with copper (Cu) ion solution provided evidence of metal ion chelation based on an observed v(Cu-O) peak at about 487 cm-1 and a v(Cu-S) signal at about 267 cm-1. The binding of Cu ions by the chelating ligands also caused a red shift of about 10 cm-1 in the Raman spectrum of the Si-(4-CMTB)-Cu surface within the spectral region, characteristic of the v(C-O) signal. X-ray photoelectron spectroscopy investigations showed indications of the Cu(II) ion species chelated by the surface-bound carboxymethylthio ligands. The functionalized surface, Si-(4-CMTB), constitutes an alternative metal ion chelating surface that may potentially be developed for applications in trace-level trapping of Cu ions.

Localized Synthesis of Conductive Copper-Tetracyanoquinodimethane Nanostructures in Ultrasmall Microchambers for Nanoelectronics.

In this work, the microfluidic-assisted synthesis of copper-tetracyanoquinodimethane (Cu-TCNQ) nanostructures in an ambient environment is reported for the first time. A two-layer microfluidic device comprising parallel actuated microchambers was used for the synthesis and enabled excellent fluid handling for the continuous and multiple chemical reactions in confined ultrasmall chambers. Different precautions were applied to ensure the reduction state of copper (Cu) for the synthesis of Cu-TCNQ charge-transfer compounds. The localized synthesis of Cu and in situ transformation to Cu-TCNQ complexes in solution were achieved by applying different gas pressures in the control layer. Additionally, various diameters of the Cu-TCNQ nano/microstructures were obtained by adjusting the concentration of the precursors and reaction time. After the synthesis, platinum (Pt) microelectrode arrays, which were aligned at the microchambers, could enable the in situ measurements of the electronic properties of the synthesized nanostructures without further manipulation. The as-prepared Cu-TCNQ wire bundles showed good conductivity and a reversible hysteretic switching effect, which proved the possibility in using them to build advanced nanoelectronics.

Fast IR laser mapping ellipsometry for the study of functional organic thin films.

Fast infrared mapping with sub-millimeter lateral resolution as well as time-resolved infrared studies of kinetic processes of functional organic thin films require a new generation of infrared ellipsometers. We present a novel laboratory-based infrared (IR) laser mapping ellipsometer, in which a laser is coupled to a variable-angle rotating analyzer ellipsometer. Compared to conventional Fourier-transform infrared (FT-IR) ellipsometers, the IR laser ellipsometer provides ten- to hundredfold shorter measurement times down to 80 ms per measured spot, as well as about tenfold increased lateral resolution of 120 µm, thus enabling mapping of small sample areas with thin-film sensitivity. The ellipsometer, equipped with a HeNe laser emitting at about 2949 cm(-1), was applied for the optical characterization of inhomogeneous poly(3-hexylthiophene) [P3HT] and poly(N-isopropylacrylamide) [PNIPAAm] organic thin films used for opto-electronics and bioapplications. With the constant development of tunable IR laser sources, laser-based infrared ellipsometry is a promising technique for fast in-depth mapping characterization of thin films and blends.

Electrochemical functionalization of gold and silicon surfaces by a maleimide group as a biosensor for immunological application.

In the present study we investigated the preparation of biofunctionalized surfaces using the direct electrochemical grafting of maleimidophenyl molecules with subsequent covalent immobilization of specific peptide to detect target antibody, thereby extending the application of the biosensing systems towards immunodiagnostics. Para-maleimidophenyl (p-MP) functional groups were electrochemically grafted on gold and silicon surfaces from solutions of the corresponding diazonium salt. A specially synthesized peptide modified with cysteine (Cys-peptide) was then immobilized on the p-MP grafted substrates by cross-linking between the maleimide groups and the sulfhydryl group of the cysteine residues. Accordingly, the Cys-peptide worked as an antigen that was able to bind specifically the target antibody (anti-GST antibody), while it was non-sensitive to a negative contrast antibody (i.e. anti-Flag ß). The immobilization of both specific and non-specific antibodies on the Cys-peptide-modified surfaces was monitored by infrared spectroscopic ellipsometry, a quartz crystal microbalance integrated in flow injection analysis system and potentiometric response. The results obtained clearly demonstrated that the direct modification of a surface with maleimidophenyl provides a very simple and reliable way of preparing biofunctionalized surfaces suitable for the construction of immunological biosensors.

Infrared spectroscopic study of the amidation reaction of aminophenyl modified Au surfaces and p-nitrobenzoic acid as model system.

We have investigated the fundamental amidation reaction by a model system consisting of an electrochemically functionalised Au surface by aminophenyl and 4-nitrobenzoic acid activated by EEDQ. The development of the NO(2) related stretching vibrations with time reveals that the amidation process is very slow at Au surfaces and is completed after about 2 days.