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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

The study of biomolecules in their native environments is a challenging task because of the vast complexity of cellular systems. Technologies developed in the last few years for the selective modification of biological species in living systems have yielded new insights into cellular processes. Key to these new techniques are bioorthogonal chemical reactions, whose components must react rapidly and selectively with each other under physiological conditions in the presence of the plethora of functionality necessary to sustain life. Herein we describe the bioorthogonal chemical reactions developed to date and how they can be used to study biomolecules.

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Bioorthogonal Chemistry: Fishing for Selectivity in a Sea of Functionality

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Quantification of biological or biochemical processes are of utmost importance for medical, biological and biotechnological applications. However, converting the biological information to an easily processed electronic signal is challenging due to the complexity of connecting an electronic device directly to a biological environment. Electrochemical biosensors provide an attractive means to analyze the content of a biological sample due to the direct conversion of a biological event to an electronic signal. Over the past decades several sensing concepts and related devices have been developed. In this review, the most common traditional techniques, such as cyclic voltammetry, chronoamperometry, chronopotentiometry, impedance spectroscopy, and various field-effect transistor based methods are presented along with selected promising novel approaches, such as nanowire or magnetic nanoparticle-based biosensing. Additional measurement techniques, which have been shown useful in combination with electrochemical detection, are also summarized, such as the electrochemical versions of surface plasmon resonance, optical waveguide lightmode spectroscopy, ellipsometry, quartz crystal microbalance, and scanning probe microscopy. The signal transduction and the general performance of electrochemical sensors are often determined by the surface architectures that connect the sensing element to the biological sample at the nanometer scale. The most common surface modification techniques, the various electrochemical transduction mechanisms, and the choice of the recognition receptor molecules all influence the ultimate sensitivity of the sensor. New nanotechnology-based approaches, such as the use of engineered ion-channels in lipid bilayers, the encapsulation of enzymes into vesicles, polymersomes, or polyelectrolyte capsules provide additional possibilities for signal amplification. In particular, this review highlights the importance of the precise control over the delicate interplay between surface nano-architectures, surface functionalization and the chosen sensor transducer principle, as well as the usefulness of complementary characterization tools to interpret and to optimize the sensor response.

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Electrochemical Biosensors - Sensor Principles and Architectures

Dissecting complex cellular processes requires the ability to track biomolecules as they function within their native habitat. Although genetically encoded tags such as GFP are widely used to monitor discrete proteins, they can cause significant perturbations to a protein's structure and have no direct extension to other classes of biomolecules such as glycans, lipids, nucleic acids and secondary metabolites. In recent years, an alternative tool for tagging biomolecules has emerged from the chemical biology community—the bioorthogonal chemical reporter. In a prototypical experiment, a unique chemical motif, often as small as a single functional group, is incorporated into the target biomolecule using the cell's own biosynthetic machinery. The chemical reporter is then covalently modified in a highly selective fashion with an exogenously delivered probe. This review highlights the development of bioorthogonal chemical reporters and reactions and their application in living systems.

Chemistry in living systems.

Protein biochips are at the heart of many medical and bioanalytical applications. Increasing interest has been focused on surface activation and subsequent functionalization strategies for immobilizing these biomolecules. Different approaches using covalent and noncovalent chemistry are reviewed; particular emphasis is placed on the chemical specificity of protein attachment and on retention of protein function. Strategies for creating protein patterns (as opposed to protein arrays) are also outlined. An outlook on promising and challenging future directions for protein biochip research and applications is also offered.

Chemical Strategies for Generating Protein Biochips

Performance of antibody microarrays fabricated by either DNA-directed immobilization, direct spotting, or streptavidin–biotin attachment: a comparative study

Staudinger-Ligation: A new Immobilization Strategy for the Preparation of Small Molecule Arrays

Diels-Alder ligation and surface immobilization of proteins.

A sticky situation: A site-specific immobilization of proteins onto a glass surface may allow the creation of protein microarrays. This approach relies on the Staudinger ligation between azide-modified proteins and a phosphane-functionalized glass surface.

Hendrik Schröder

Papers

Chemical Strategies for Generating Protein Biochips

Performance of antibody microarrays fabricated by either DNA-directed immobilization, direct spotting, or streptavidin–biotin attachment: a comparative study

Staudinger-Ligation: A new Immobilization Strategy for the Preparation of Small Molecule Arrays

Diels-Alder ligation and surface immobilization of proteins.

Site‐Selective Protein Immobilization by Staudinger Ligation