Efficient capture and simple quantification of circulating tumor cells using quantum dots and magnetic beads.

Circulating tumor cells (CTCs) are valuable biomarkers for monitoring the status of cancer patients and drug efficacy. However, the number of CTCs in the blood is extremely low, and the isolation and detection of CTCs with high efficiency and sensitivity remain a challenge. Here, we present an approach to the efficient capturing and simple quantification of CTCs using quantum dots and magnetic beads. Anti-EpCAM antibody-conjugated quantum dots are used for the targeting and quantification of CTCs, and quantum-dot-attached CTCs are isolated using anti-IgG-modified magnetic beads. Our approach is shown to result in a capture efficiency of about 70%-80%, enabling the simple quantification of captured CTCs based on the fluorescence intensity of the quantum dots. The present method can be used effectively in the capturing and simple quantification of CTCs with high efficiency for cancer diagnosis and monitoring.

Ambient-ageing processes in amine self-assembled monolayers on microarray slides as studied by ToF-SIMS with principal component analysis, XPS, and NEXAFS spectroscopy.

We investigated the ageing of amine-terminated self-assembled monolayers (amine-SAMs) on different silica substrates due to exposure to different ambient gases, pressures, and/or temperatures using time-of-flight secondary ion mass spectrometry (ToF-SIMS) with principal component analysis and complementary methods of surface analysis as X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS). The goal of this study is to examine the durability of primary amine groups of amine-SAMs stored in a user laboratory prior to being used as supports for biomolecule immobilization and other applications. We prepared amine-SAMs on the native oxides of silicon wafers and glass slides using 3-aminopropyl triethoxysilane, by using optimized conditions such as anhydrous organic solvent and reaction time scale of hours to avoid multilayer growth. Selected commercial amine-SAM slides have been investigated, too. When the amine-SAMs are exposed to air, oxygen incorporation occurs, followed by formation of amide groups. The formation of oxygen species due to ageing was proved by ToF-SIMS, XPS, and NEXAFS findings such as CNO(-) secondary ion emission at m/z 42, observation of the N 1s HNC=O component peak at 400.2-400.3 eV in XPS, and, last but not least, by formation of a π*(HNC=O) resonance at 401 eV in the N K-edge X-ray absorption spectrum. It is concluded that the used multi-method approach comprising complementary ToF-SIMS, XPS, and NEXAFS analyses is well suited for a thorough study of chemical aspects of ageing phenomena of amine-SAM surfaces.

Adlayers of dimannoside thiols on gold: surface chemical analysis.

Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C-O) and acetal moieties (O-C-O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.

Selective and direct immobilization of cysteinyl biomolecules by electrochemical cleavage of azo linkage.

Controlled orientation and reserved activity of biomolecules, when site-selectively immobilized in a highly integrated manner on a minimal time scale, are crucial in designing biosensors for the multiplex detection. Here, we describe a novel method for the orientation-controlled immobilization of biomolecules based on site-selective electrochemical activation of p-hydroxyazobenzene self-assembled monolayer (SAM) followed by one-step coupling of cysteinyl biomolecules. The p-aminophenol, a product of reductive cleavage of p-hydroxyazobenzene, was subsequently oxidized to yield p-quinoneimine which then conjugated with cysteinyl biomolecules through 1,4-Michael addition, thus obviating additional linker agents and the related time consumption. Using this method, we selectively activated the electrode surface and immobilized laminin peptide IKVAV, a neurite promoting motif. When we cultured hippocampal neurons on the electrode, the extended neurites were found only within the electrochemically activated area. Hence, the proposed method represents a new promising platform for the patterning of functional peptides, active proteins, and live cells.

Electrochemical cleavage of azo linkage for site-selective immobilization and cell patterning.

A new molecular structure of azobenzene, which can be reduced to the corresponding anilines at a low reduction potential for the site-selective immobilization of biomolecules, is proposed. Redox-active species, enzymes, peptides, and cultured hippocampal neurons can be effectively immobilized on the electrochemically activated surface.