Covalent organic frameworks (COFs) represent an exciting new type of porous organic materials, which are ingeniously constructed with organic building units via strong covalent bonds. The well-defined crystalline porous structures together with tailored functionalities have offered the COF materials superior potential in diverse applications, such as gas storage, adsorption, optoelectricity, and catalysis. Since the seminal work of Yaghi and co-workers in 2005, the rapid development in this research area has attracted intensive interest from researchers with diverse expertise. This critical review describes the state-of-the-art development in the design, synthesis, characterisation, and application of the crystalline porous COF materials. Our own opinions on further development of the COF materials are also presented for discussion (155 references).

Covalent organic frameworks (COFs): from design to applications

Surface-enhanced Raman scattering (SERS) has become a mature vibrational spectroscopic technique during the last decades and the number of applications in the chemical, material, and in particular life sciences is rapidly increasing. This Review explains the basic theory of SERS in a brief tutorial and-based on original results from recent research-summarizes fundamental aspects necessary for understanding SERS and provides examples for the preparation of plasmonic nanostructures for SERS. Chemical applications of SERS are the centerpiece of this Review. They cover a broad range of topics such as catalysis and spectroelectrochemistry, single-molecule detection, and (bio)analytical chemistry.

Surface-enhanced Raman spectroscopy: concepts and chemical applications.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

/pdf/present-and-future-of-surface-enhanced-raman-scattering-34aqgcm385.pdf

Present and Future of Surface-Enhanced Raman Scattering

Dingcai Wu,*,† Fei Xu,† Bin Sun,† Ruowen Fu,† Hongkun He,‡ and Krzysztof Matyjaszewski*,‡ †Materials Science Institute, Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, People's Republic of China ‡Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States

Design and Preparation of Porous Polymers

CONTENTS 1. Introduction 1.1. Fundamental Theory of Surface-Enhanced Raman Scattering 1.2. Optical Properties of SERS Tags 2. Synthesis of SERS Tags 2.1. Noble Metal Nanosubstrates 2.1.1. Single Particle-Based SERS Substrates 2.1.2. Nanoparticle Cluster-Based Substrates 2.2. Raman Reporter Molecules 2.2.1. Selection Principles and Reporter Types 2.2.2. Self-Assembled Monolayer Coverage Strategy 2.3. Surface Coating for Protection 2.3.1. Biomolecule Coating 2.3.2. Polymer Coating 2.3.3. Liposome Coating 2.3.4. Silica Coating 2.4. Attachment of Targeting Molecules 3. Bioanalysis Applications 3.1. Ionic and Molecular Detection 3.2. Pathogen Detection 3.3. Live-Cell Imaging 3.3.1. Cancer Marker Detection 3.3.2. Intercellular Microenvironment Sensing 3.4. Tissue SERS Imaging 3.5. In Vivo SERS Imaging 4. Challenges and Perspectives 4.1. Reproducible Signal of SERS Tags 4.1.1. Precisely Controlled Hot Spots for Nanosubstrates 4.1.2. Calibration of SERS Intensities and Enhancements 4.2. Improving Multiplexing Capability 4.3. Reduced Size for Subcellular Imaging 4.4. Development of Multifunctional Nanoplatforms 4.4.1. Magnetic SERS Dots 4.4.2. Multimodal Imaging Dots 4.4.3. SERS Tag-Based Therapeutic Systems 4.5. Biocompatibility 5. Conclusions and Remarks

SERS Tags: Novel Optical Nanoprobes for Bioanalysis

After over 30 years of development, surface-enhanced Raman spectroscopy (SERS) is now facing a very important stage in its history. The explosive development of nanoscience and nanotechnology has assisted the rapid development of SERS, especially during the last 5 years. Further development of surface-enhanced Raman spectroscopy is mainly limited by the reproducible preparation of clean and highly surface enhanced Raman scattering (SERS) active substrates. This review deals with some substrate-related issues. Various methods will be introduced for preparing SERS substrates of Ag and Au for analytical purposes, from SERS substrates prepared by electrochemical or vacuum methods, to well-dispersed Au or Ag nanoparticle sols, to nanoparticle thin film substrates, and finally to ordered nanostructured substrates. Emphasis is placed on the analysis of the advantages and weaknesses of different methods in preparing SERS substrates. Closely related to the application of SERS in the analysis of trace sample and unknown systems, the existing cleaning methods for SERS substrates are analyzed and a combined chemical adsorption and electrochemical oxidation method is proposed to eliminate the interference of contaminants. A defocusing method is proposed to deal with the laser-induced sample decomposition problem frequently met in SERS measurement to obtain strong signals. The existing methods to estimate the surface enhancement factor, a criterion to characterize the SERS activity of a substrate, are analyzed and some guidelines are proposed to obtain the correct enhancement factor.

Surface-enhanced Raman spectroscopy: substrate-related issues

Layered core−shell bimetallic silver−gold nanoparticles were prepared by coating Au layers over Ag seeds by a seed-growth method. The composition of Ag100-xAux particles can vary from x = 0 to 30. TEM and SEM images clearly show that the bimetallic nanoparticles are of core−shell structure with some pinholes on the surface. Strong surface-enhanced Raman (SER) signals of thiophenol and p-aminothiophenol have been obtained with these colloids. It was found that the SERS activity of aggregated colloids critically depends on the molar ratio of Ag to Au. With the increase of the Au molar fraction, the SERS activity enhances first and then weakens, with the maximal intensity being 10 times stronger than that of Ag colloids. The AgcoreAushell nanoparticles were then labeled with monoclonal antibodies and SERS probes and used for immunoassay analysis. In the proposed system, antibodies immobilized on a solid substrate can interact with the corresponding antigens to form a composite substrate, which can capture re...

Synthesis of AgcoreAushell bimetallic nanoparticles for immunoassay based on surface-enhanced Raman spectroscopy

Targeted synthesis of a 3D porous aromatic framework for selective sorption of benzene.

Local microenvironment pH sensing is one of the key parameters for the understanding of many biological processes. As a noninvasive and high sensitive technique, surface-enhanced Raman spectroscopy (SERS) has attracted considerable interest in the detection of the local pH of live cells. We herein develop a facile way to prepare Au-(4-MPy)-BSA (AMB) pH nanosensor. The 4-MPy (4-mercaptopyridine) was used as the pH sensing molecule. The modification of the nanoparticles with BSA not only provides a high sensitive response to pH changes ranging from pH 4.0 to 9.0 but also exhibits a high sensitivity and good biocompatibility, stability, and reliability in various solutions (including the solutions of high ionic strength or with complex composition such as the cell culture medium), both in the aggregation state or after long-term storage. The AMB pH nanosensor shows great advantages for reliable intracellular pH analysis and has been successfully used to monitor the pH distribution of live cells and can address the grand challenges in SERS-based pH sensing for practical biological applications.

BSA-coated nanoparticles for improved SERS-based intracellular pH sensing.

The increasing application of nanomaterials in biosensor and imaging sets a higher demand on the multifunctionalities of nanomaterials for obtaining multiple parameters of a same system under a same condition. In this work, multifunctional Au@organosilica nanoparticles with high stability were conveniently synthesized by direct hydrolyzing of 3-mercaptopropyltriethoxysilane in an aqueous solution in the presence of a Au core. Modification of the Au core with Raman reporters and the organosilica shell with fluorophore before and after the hydrolysis, respectively, produces multifunctional nanoparticles exhibiting Rayleigh scattering of the Au core, fluorescence signals of the fluorophores and surface-enhanced Raman scattering (SERS) of the Raman reporters. The nanoparticles can be used as multimodal tracers for living cell imaging and related biological research.

Yan Cui

Papers

Surface-enhanced Raman spectroscopy: substrate-related issues

Synthesis of AgcoreAushell bimetallic nanoparticles for immunoassay based on surface-enhanced Raman spectroscopy

Targeted synthesis of a 3D porous aromatic framework for selective sorption of benzene.

BSA-coated nanoparticles for improved SERS-based intracellular pH sensing.

Au@organosilica multifunctional nanoparticles for the multimodal imaging