Session J26: Focus Session: At the Interface of Molecules and Materials II

Corona Phase Molecular Recognition (CoPhMoRe) to Enable New Nanosensor Interfaces

Our lab at MIT has been interested in how the 1D and 2D electronic structures of carbon nanotubes and graphene respectively can be utilized to advance new concepts in molecular detection. We introduce CoPhMoRe or corona phase molecular recognition [1] as a method of discovering synthetic antibodies, or nanotube-templated recognition sites from a heteropolymer library. We show that certain synthetic heteropolymers, once constrained onto a single-walled carbon nanotube by chemical adsorption, also form a new corona phase that exhibits highly selective recognition for specific molecules. To prove the generality of this phenomenon, we report three examples of heteropolymers--nanotube recognition complexes for riboflavin, L-thyroxine and estradiol. The platform opens new opportunities to create synthetic recognition sites for molecular detection. We have also extended this molecular recognition technique to neurotransmitters, producing the first fluorescent sensor for dopamine. Another area of advancement in biosensor development is the use of near infrared fluorescent carbon nanotube sensors for in-vivo detection [2]. Here, we show that PEG-ligated d(AAAT)$_{\mathrm{7}}$ DNA wrapped SWNT are selective for nitric oxide, a vasodilator of blood vessels, and can be tail vein injected into mice and localized within the viable mouse liver. We use an SJL mouse model to study liver inflammation in vivo using the spatially and spectrally resolved nIR signature of the localized SWNT sensors. \\[4pt] [1] Zhang, JQ et. al. Molecular recognition using corona phase complexes made of synthetic polymers adsorbed on carbon nanotubes. Nature Nanotechnology, 8, 12, 2013, 959-968\\[0pt] [2] Iverson, NM, et. al. In vivo biosensing via tissue-localizable near-infrared-fluorescent single-walled carbon nanotubes. Nature Nanotechnology, 8, 11, 2013, 873-880   

Detection of DNA and Protein using CVD Graphene-channel FET Biosensors

Graphene channel field-effect biosensors are demonstrated for detecting the binding of double-stranded DNA and poly-l-lysine. Sensors consist of CVD graphene transferred using a clean, etchant-free transfer method. The presence of DNA and poly-l-lysine are detected by the change in the Dirac Voltage (the voltage at which the graphene's resistance peaks) of the graphene transistor. Sensors show large shifts in the Dirac voltage $\sim$ 17 V after exposure to $\sim$ 580 pM of poly-l-lysine and $\sim$ 14 V upon exposure to 300 pM of DNA. The polarity of the response changes to positive direction with poly-l-lysine and negative direction with DNA. Sensors show detection limits of 8 pM for 48.5 kbp DNA and 11 pM for poly-l-lysine. The biosensors are easy to fabricate, reusable and are promising as sensors of a wide variety of charged biomolecules.   

High Yield and Scalable Fabrication of Nano/Bio Hybrid Graphene Field Effect Transistors for Cancer Biomarker Detection

Graphene field effect transistors (GFETs) hold tremendous promise for use as biosensor transduction elements due to graphene's high mobility, low noise and all-surface structure with every atom exposed to the environment. We developed a GFET array fabrication based on two approaches, pre-patterned transfer and post-transfer photolithography. Both approaches are scalable, high yield, and electrically stable. Functional groups for protein immobilization were added to the GFET using various bi-functional pyrene-based linkers. One approach immobilized an azide engineered protein through a ``Staudinger Reaction'' chemistry with NHS-phosphine reacting with a 1-aminopyrene linker. Another approach bound an engineered antibody via 1-pyrene butanoic acid succinimidyl ester, where an amine group of the antibody reacts to the succinimide of the linker. GFETs were studied by Raman spectroscopy, AFM and current-gate voltage (I-Vg) characterization at several steps of the fabrication process. A sensing response was obtained for a breast cancer biomarker (HER2) as a function of target concentration. We have started to design multiplexed sensor arrays by adding several functional groups to GFETs on a single chip. Simultaneous detection with these devices will be discussed.   

Infrared detection with colloidal quantum dots based on interband and intraband transitions

While much research on colloidal quantum dots is focused on their potential as visible emitter or light harvester, this talk will cover our investigations of the mercury chalcogenide colloidal quantum dots in the thermal mid-infrared ranges of 3-5 microns and 8-12 microns where the atmosphere is transparent. HgTe is a zero-gap semiconductor. As a result, colloidal quantum dots (CQD) of sizes between 10 and 20 nm readily lead to infrared gaps tuning between 3 and 12 microns respectively. It is also very promising that infrared photodetection using dried films of these CQDs has now been demonstrated up to 12 microns. Further improvement through chemistry are likely and will be required to raise the detectivity to the level required to transform thermal infrared detection technology. In contrast to HgTe CQDs which tend to be intrinsic, beta-HgS and HgSe CQDs are naturally n-doped, in the first such instance with CQDs. Furthermore, the doping is modulated by modifying the surface composition, and this effect is attributed to the tuning of the energy level with respect to the environment, via the surface electrostatics. With controlled doping, both HgSe and HgS CQDs have now led to the first operation of mid-infrared CQD photodetector based on the intraband absorption. This is a breakthrough in the field of colloidal quantum dots where interband transitions had been exclusively used for the past 30 years. One challenge with both interband and intraband infrared CQDs will be to reduce the nonradiative recombination, which will improve the detectivity as well as allow to use their infrared luminescence.   

Unraveling Molecular Structure in Stern Layer at Charged Water Interface using sum-frequency vibrational spectroscopy

Charged aqueous interfaces, such as membrane/water and electrochemical interfaces, are essential in many chemical, biological, and environmental processes. Interactions between heterogeneous interfacial molecules and the consequent molecular network dictate properties and functions of the interfaces; however, the microscopic-level picture of the charged water interfaces remains substantially unclear. Here we demonstrate probing of the molecular structure in Stern layer at aqueous interfaces using sum-frequency vibrational spectroscopy. We show that at ionic surfactant/water interfaces, the hydrogen- (H-)bonding strength and network in the Stern layer depend sensitively on conformation and ionization of the surfactants, suggesting a relevant influence of the surfactant-water charge transfer. In addition, ion adsorption to the interface is shown to distort the interfacial water structure. Our study offers exciting opportunities to acquire microscopic insights into interfaces for catalytic and electrochemical applications.   

Mind the Entropy: Electronic and Thermal Fluctuations of Large Molecules on Metals

The prevailing working hypothesis in vacuum surface science is that equilibrium properties of adsorbed molecules are largely unaltered by finite temperature effects. In this work we illustrate that this is not the case for the adsorption geometry, energetics, and desorption temperature of the molecular switch Azobenzene adsorbed to Ag(111). Comparing with X-ray standing wave measurements and temperature programmed desorption experiments we find strong discrepancies to static Density-Functional Theory calculations. Anharmonic corrections and ab-initio molecular dynamics simulation of the free energy of desorption account for the thermal fluctuations and inclusion of many-body dispersion effects accounts for the electronic fluctuations that govern the interaction strength. In both cases more modest, typically employed approaches fail to capture the sizable entropy of desorption and the correct desorption temperature. This implies that an accurate description of adsorbate interactions and entropies of adsorption in most realistic functional hybrid metallic organic systems necessitates a full account of the inherent anharmonicity of adsorbate and substrate in addition to an accurate description of dispersion interactions.   

Stressed and Compressed Polymersomes

Polymersomes are well-defined vesicular structures that have been studied extensively for encapsulation, controlled release and as cell mimics, inter alia. While polymersomes at ambient conditions are reasonably well-understood, comparatively little is known about how structure and properties change when subject to variations in their local environment. In this talk, atomic force microscopy is used to probe PEO-PBD polymersomes adsorbed at a solid liquid interface under osmotic pressure. We reveal interesting changes in shape and solvation not captured by classical theory.   

Effect of CO$_{2}$ on a polystyrene adsorbed nanolayer

We report the role of compressed carbon dioxide (CO$_{2}$) in a mobility gradient of polymer chains near a planar solid substrate. A series of bilayers of bottom hydrogenated polystyrene and top deuterated polystyrene layers were prepared on Si substrates, and high pressure neutron reflectivity (NR) was used to study diffusive motion at the polymer/polymer interface. The interdiffusion is hindered when the distance is less than 3Rg (Rg, radius of polymer gyration). This reduced chain diffusivity is attributed to CO$_{2}$-induced polymer adsorption on the substrate, transforming the 0.6Rg thick region from the substrate interface into an irreversibly adsorbed polymer layer. The cohesion strength is attributed to loops in the adsorbed chains with which the neighboring chains can entangle.   

First-principles investigation of CO2 absorption on III-nitride surfaces

Photon-induced chemical transformation of CO2 is a very interesting direction of green-house gas reduction. An accurate description of electronic structure at the interface between CO2 and the photocatalytics is important for understanding the process of artificial photosynthesis. In this work we report density functional theory (DFT) and many-body GW calculations to investigate CO2 adsorption on III-nitride semiconductor surface. The adsorption geometry is determined at the DFT level and the electronic structure is investigated at both DFT and GW levels. A detailed illustration of how the molecular orbital is renormalized is addressed.   

\textit{Ab inito} molecular-dynamics study of EC decomposition process on Li$_{2}$O$_{2}$ surfaces

We have simulated electrochemical reactions of the EC molecule decomposition on Li$_{2}$O$_{2}$ substrate by \textit{ab initio} molecular dynamics combined with the effective screening medium method. EC molecules adsorb onto the peroxide spontaneously. We find through the analysis of density of states that the adsorption state is stabilized by hybridization of the \textit{sp2} orbital and the surface states of the Li$_{2}$O$_{2}$. After adsorption, EC ring opens, which leads to the decomposition of the peroxide and the formation of a carboxy group. This kind of alkyl carbonates formed on the Li$_{2}$O$_{2}$ substrate was found in experiments actually   

Understanding 3C-SiC/SiO$_2$ interfaces in SiC-nanofiber based solar cells from \emph{ab initio} theory

Nanostructured materials -- such as e. g. hybrid nanocomposites consisting of inorganic semiconducting nanofibers and organic surfactants -- provide genuinely novel pathways to exceed the Shockley-Queisser limit for solar energy conversion. The synthesis of such functionalized nanofibers can be performed completely using only inexpensive wet chemical solution processing. However, the synthesis conditions often lead to complex interfacial structures involving thin oxide layers between the nanofiber and surfactants, whose atomistic details are poorly understood at best. Here we present a combined density functional theory and tight binding investigation of interfaces between 3C-SiC nanofiber surfaces and SiO$_2$. Considering a wide variety of possible interfacial structures we utilize a grand canonical approach to generate a phase diagram and predict the structural details of the interface as a function of the chemical potentials of Si, O and H. This study provides directions about how the synthesis conditions lead to specific types of interfacial structures and their impact on the electronic properties of the interface.