Titanium Carboxylate Molecular Layer Deposited Hybrid Films as Protective Coatings for Lithium-Ion Batteries.

The lifetime of lithium-ion batteries can be extended by applying protective coatings to the cathode's surface. Many studies explore atomic layer deposition (ALD) for this purpose. However, the complementary molecular layer deposition (MLD) technique might offer the benefit of depositing hybrid coatings that are flexible and can accommodate potential volume changes of the electrode during charging and discharging of the battery. This study reports the deposition of titanium carboxylate thin films via MLD. The structure and stability of the hybrid films are studied by using Fourier transform IR spectroscopy. The electrochemical properties of two titanium carboxylate films and a "titanicone" MLD film, deposited by using TDMAT and glycerol, are evaluated on top of a TiO2, TiN, and LiMn2O4 electrode. The coatings are found to present good lithium-ion kinetics and to reduce electrolyte decomposition. Overall, the titanium carboxylate films deposited in this work seem promising as protective and elastic coatings for future high-energy lithium-ion battery cathodes.

An IR Spectroscopy Study of the Degradation of Surface Bound Azido-Groups in High Vacuum.

Controlled surface functionalization with azides to perform on surface "click chemistry" is desired for a large range of fields such as material engineering and biosensors. In this work, the stability of an azido-containing self-assembled monolayer in high vacuum is investigated using in situ Fourier transform infrared spectroscopy. The intensity of the antisymmetric azide stretching vibration is found to decrease over time, suggesting the degradation of the azido-group in high vacuum. The degradation is further investigated at three different temperatures and at seven different nitrogen pressures ranging from 1 × 10-6 mbar to 5 × 10-3 mbar. The degradation is found to increase at higher temperatures and at lower nitrogen pressures. The latter supporting the theory that the degradation reaction involves the decomposition into molecular nitrogen. For the condition with the highest degradation detected, only 63% of azides is found to remain at the surface after 8 h in vacuum. The findings show a significant loss in control of the surface functionalization. The instability of azides in high vacuum should therefore always be considered when depositing or postprocessing azido-containing layers.

Chemical Vapor Deposition of Azidoalkylsilane Monolayer Films.

N3-functionalized monolayers on silicon wafer substrates are prepared via the controlled vapor-phase deposition of 11-azidoundecyltrimethoxysilanes at reduced pressure and elevated temperature. The quality of the layer is assessed using contact angle, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and ellipsometry measurements. At 60 °C, longer deposition times are needed to achieve monolayers with similar N3 density compared to depositions at 145 °C. The monolayers formed via the vapor phase are denser compared to those formed via a solvent-based deposition process. ATR-FTIR measurements confirm the incorporation of azido-alkyl chains in the monolayer and the formation of siloxane bridges with the underlying oxide at both deposition temperatures. X-ray photon spectroscopy shows that the N3 group is oriented upward in the grafted layer. Finally, the density was determined using total reflection X-ray fluorescence after a click reaction with chlorohexyne and amounts to 2.5 × 1014 N3 groups/cm2. In summary, our results demonstrate the formation of a uniform and reproducible N3-containing monolayer on silicon wafers, hereby providing a functional coating that enables click reactions at the substrate.

Full-wafer in-situ fabrication and packaging of microfluidic flow cytometer with photo-patternable adhesive polymers.

Integration of microelectronics with microfluidics enables sophisticated lab-on-a-chip devices for sensing and actuation. In this paper, we investigate a novel method for in-situ microfluidics fabrication and packaging on wafer level. Two novel photo-patternable adhesive polymers were tested and compared, PA-S500H and DXL-009. The microfluidics fabrication method employs photo lithographical patterning of spin coated polymer films of PA or DXL and direct bonding of formed microfluidics to a top glass cover using die-to-wafer level bonding. These new adhesive materials remove the need for additional gluing layers. With this approach, we fabricated disposable microfluidic flow cytometers and evaluated the performance of those materials in the context of this application. DXL-009 exhibits lower autofluorescence compared to PA-S500H which improves detection sensitivity of fluorescently stained cells. Results obtained from the cytotoxicity test reveals that both materials are biocompatible. The functionality of these materials was demonstrated by detection of immunostained monocytes in microfluidic flow cytometers. The flexible, fully CMOS compatible fabrication process of these photo-patternable adhesive materials will simplify prototyping and mass manufacturing of sophisticated microfluidic devices with integrated microelectronics.

Multiplexed site-specific electrode functionalization for multitarget biosensors.

Multitarget biosensors hold great promise to improve point-of-care diagnostics as they enable simultaneous detection of different biomolecular markers. Multiplexed detection of different markers, like genes, proteins, or a combination of both, propels advancement in numerous fields such as genomics, medical diagnosis and therapy monitoring. The functionalization of these biosensors, however, necessitates patterned immobilization of different bioreceptors, which remains challenging and time-consuming. We demonstrate a simple method for the patterned multiplexing of bioreceptors on a multi-electrode chip. By using the lithographically defined electrodes for surface functionalization, additional patterning steps become obsolete. Using the electrodes for self-aligned immobilization provides a spatial resolution that is limited by the electrode patterning process and that cannot be easily obtained by alternative dispensing or coating techniques. Via electrochemical reduction of diazonium salts combined with click chemistry, we achieved site-specific immobilization of two different ssDNA probes side by side on a single chip. This method was experimentally verified by cyclic voltammetry (CV), Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), and specific target recognition was visualized by fluorescence microscopy. The combination of the electroaddressability of electrografting with the chemoselectivity of click chemistry, offers a versatile platform for highly efficient site-specific functionalization of multitarget biosensors.

Integration of clinical point-of-care requirements in a DNA microarray genotyping test.

Various proof-of-concept studies have shown the potential of biosensors with a high multiplex detection capability for the readout of DNA microarrays in a lab-on-a-chip. This is particularly interesting for the development of point-of-care genotyping tests, to screen for multiple pathogens and/or antibiotic resistance patterns. In this paper, an assay workflow is presented, suited for the development of novel lab-on-a-chips with an integrated DNA microarray. Besides the description of the different assay steps (DNA purification, amplification and detection), a control strategy is presented according to recommendations of the US Food and Drug Administration (FDA). To use a lab-on-a-chip for diagnostic applications, the optimization and evaluation of the assay performance with clinical samples is very important. Therefore, appropriate quantification methods are described, which allow optimization and evaluation of the separate assay steps, as well as total assay performance. In order to demonstrate and evaluate the total workflow, blood samples spiked with Streptococcus pneumoniae were tested. All blood samples with ≥ 10(3)CFU S. pneumoniae per ml of human blood were successfully detected by this genotyping assay.

Specific cell targeting with nanobody conjugated branched gold nanoparticles for photothermal therapy.

Branched gold nanoparticles are potential photothermal therapy agents because of their large absorption cross section in the near-infrared window. Upon laser irradiation they produce enough heat to destroy tumor cells. In this work, branched gold nanoparticles are biofunctionalized with nanobodies, the smallest fully functional antigen-binding fragments evolved from the variable domain, the VHH, of a camel heavy chain-only antibody. These nanobodies bind to the HER2 antigen which is highly expressed on breast and ovarian cancer cells. Flow cytometric analysis and dark field images of HER2 positive SKOV3 cells incubated with anti-HER2 conjugated branched gold nanoparticles show specific cell targeting. Laser irradiation studies reveal that HER2 positive SKOV3 cells exposed to the anti-HER2 targeted branched gold nanoparticles are destroyed after five minutes of laser treatment at 38 W/cm(2) using a 690 nm continuous wave laser. Starting from a nanoparticle optical density of 4, cell death is observed, whereas the control samples, nanoparticles with anti-PSA nanobodies, nanoparticles only, and laser only, do not show any cell death. These results suggest that this new type of bioconjugated branched gold nanoparticles are effective antigen-targeted photothermal therapeutic agents for cancer treatment.

Label-free genosensor based on immobilized DNA hairpins on gold surface.

In this report, we demonstrate a label-free genosensor based on DNA hairpins coupled to gold coated sensor surfaces. The hairpin probes were labeled with a thiolated moiety for immobilization at the 5' end and with a fluorophore for signal transduction at the 3' end. In the absence of the complement, the fluorophore is quenched by energy transfer to the gold surface. Addition of the target sequence leads to the hairpin unfolding, and releases the fluorescent signal. This built-in property, using a gold film as both the immobilizing substrate and quenching agent, has the advantage of simplicity in design and ease of further integration. Our results showed that lengths of both the stem and the loop structures have significant effects on the sensor performance. Hybridization kinetics was investigated for various probe/target lengths and concentrations. An optimized hairpin probe gave a fluorescent signal increase of 39 folds after hybridization, which is much higher than the earlier reported results. A limit of detection (LOD) down to 0.3 nM for the complementary target DNA detection has been achieved. The developed sensor was further successfully applied for the detection of single-base mismatch targets, as well as for the direct detection of PCR products.

A simple double-bead sandwich assay for protein detection in serum using UV-vis spectroscopy.

In this study a double-bead sandwich assay, employing magnetic nanoparticles and gold nanoparticles is proposed. The magnetic nanoparticles allow specific capturing of the analyte in biological samples, while the optical properties of the gold nanoparticles provide the signal transduction. We demonstrated that a major improvement in the assay sensitivity was obtained by selecting an optimal gold nanoparticle size (60 nm). A detection limit of 5-8 ng/mL, a sensitivity of 0.6-0.8 (pg/mL)(-1) and a dynamic range of 3 orders of magnitude were achieved without any further amplification using the detection of prostate specific antigen in serum as a model system. The proposed assay has the ability to be easily implemented within a microfluidic device for point-of-care applications whereby the readout can be executed by a fast and cheap optical measurement.

Poly(acrylic acid)-stabilized colloidal gold nanoparticles: synthesis and properties.

Combining the intriguing optical properties of gold nanoparticles with the inherent physical and dynamic properties of polymers can give rise to interesting hybrid nanomaterials. In this study, we report the synthesis of poly(acrylic acid) (PAA)-capped gold nanoparticles. The polyelectrolyte-wrapped gold nanoparticles were fully characterized and studied via a combination of techniques, i.e. UV-vis and infrared spectroscopy, dark field optical microscopy, SEM imaging, dynamic light scattering and zeta potential measurements. Although PAA-capped nanoparticles have been previously reported, this study revealed some interesting aspects of the colloidal stability and morphological change of the polymer coating on the nanoparticle surface in an electrolytic environment, at various pH values and at different temperatures.

Fiber optic SPR biosensing of DNA hybridization and DNA-protein interactions.

In this paper we present a fiber optic surface plasmon resonance (SPR) sensor as a reusable, cost-effective and label free biosensor for measuring DNA hybridization and DNA-protein interactions. This is the first paper that combines the concept of a fiber-based SPR system with DNA aptamer bioreceptors. The fibers were sputtered with a 50nm gold layer which was then covered with a protein repulsive self-assembled monolayer of mixed polyethylene glycol (PEG). Streptavidin was attached to the PEG's carboxyl groups to serve as a versatile binding element for biotinylated ssDNA. The ssDNA coated SPR fibers were first evaluated as a nucleic acid biosensor through a DNA-DNA hybridization assay for a random 37-mer ssDNA. This single stranded DNA showed a 15 nucleotides overlap with the receptor ssDNA on the SPR fiber. A linear calibration curve was observed in 0.5-5 microM range. A negative control test did not reveal any significant non-specific binding, and the biosensor was easily regenerated. In a second assay the fiber optic SPR biosensor was functionalized with ssDNA aptamers against human immunoglobulin E. Limits of detection (2nM) and quantification (6nM) in the low nanomolar range were observed. The presented biosensor was not only useful for DNA and protein quantification purposes, but also to reveal the binding kinetics occurring at the sensor surface. The dissociation constant between aptamer and hIgE was equal to 30.9+/-2.9nM. The observed kinetics fully comply with most data from the literature and were also confirmed by own control measurements.

Stability of mixed PEO-thiol SAMs for biosensing applications.

The secret of a successful affinity biosensor partially hides in the chemical interface layer between the transducer system and the biological receptor molecules. Over the past decade, several methodologies for the construction of such interface layers have been developed on the basis of the deposition of self-assembled monolayers (SAMs) of alkanethiols on gold. Moreover, mixed SAMs of polyethylene oxide (PEO) containing thiols have been applied for the immobilization of biological receptors. Despite the intense research in the field of thiol SAMs, relatively little is known about their biosensing properties in correlation with their long-term stability. Especially the impact of the storage conditions on their biosensing characteristics has not been reported before to our knowledge. To address these issues, we prepared mixed PEO SAMs and tested their stability and biosensing performance in several storage conditions, i.e., air, N2, ethanol, phosphate buffer, and H2O. The quality of the SAMs was monitored as a function of time using various characterization techniques such as cyclic voltammetry, contact angle, grazing angle Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the impact of the different storage conditions on the biosensor properties was investigated using surface plasmon resonance. Via the latter technique, the receptor immobilization, the analyte recognition, and the nonspecific binding were extensively studied using the prostate specific antigen as a model system. Our experiments showed that very small structural differences in the SAM can have a great impact in their final biosensing properties. In addition it was shown that the mixed SAMs stored in air or N2 are very stable and retain their biosensor properties for at least 30 days, while ethanol appeared to be the worst storage medium due to partial oxidation of the thiol headgroup. In conclusion, care must be taken to avoid SAM degradation during storage to retain typical SAM characteristics, which is very important for their general use in many proposed applications.

Engineering camel single-domain antibodies and immobilization chemistry for human prostate-specific antigen sensing.

The specificity and affinity characteristics of antibodies make them excellent probes in biosensor applications. Unfortunately, their large size, unstable behavior, and random immobilization properties create numerous problems. The single-domain antigen-binding fragment derived from heavy-chain antibodies of camelids (termed VHH) offers special advantages in terms of size, stability, and ease of generating different antibody constructs. In this study, we show the potential of those VHHs in sensing human prostate-specific antigen (hPSA) by SPR technology. Different VHH constructs were immobilized onto commercial and custom-built sensor surfaces by metal chelation, biotin-streptavidin interaction, or covalent coupling. The detection of subnanogram per milliliter hPSA concentrations could be attained on a covalently coupled three-dimensional dextran surface. Moreover, the ratio of different hPSA isoform concentrations could be assessed via a sandwich assay and resulted in the detection of clinically significant antigen concentrations within 15 min. In addition, for the first time, the intrinsic protein stability is presented as an important probe design factor, since our results reveal that higher intrinsic stability offers higher resistance to harsh regeneration conditions. In conclusion, we present VHHs as a novel class of biosensor probes rivaling conventional antibodies and their derived antibody fragments.