Aggregation-Induced Emission

Applications in Biosensing, Bioimaging and Biomedicine – Volume 1

Xinggui Gu, Ben Zhong Tang, Ben Zhong Tang, Xinggui Gu

• Publisher: De Gruyter
• Year: 2022
• ISBN:
  9783110672343
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

This two volume set introduces the up-to-date high-tech applications of Aggregation-Induced Emission (AIE) luminogens mainly in the areas of biosensing, bioimaging, and biomedicine. The 1st volume covers the applications of AIE materials in biosensing and bioimaging, including the technological utilizations in ionic/biomolecular sensing, bacterial imaging, cell imaging, intracellular microenvironment analysis, advanced optical imaging and multimodality, etc. It is an essential reference for materials scientists, chemists, physicists and biological chemists.

Chapter 1 Introduction

Engui Zhao

School of Science, Harbin Institute of Technology, Shenzhen, HIT Campus of University Town, Shenzhen, China

Hui Li

Beijing Advanced Innovation Center for Soft Matter Science and Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, China

Xinggui Gu

Beijing Advanced Innovation Center for Soft Matter Science and Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, China

Ben Zhong Tang

Shenzhen Institute of Molecular Aggregate Science and Engineering, School of Science and Engineering, The Chinese University of Hong Kong (Shenzhen), Shenzhen, China

As human living standard improves, healthcare and medicine have drawn increasing attention from both scientists and ordinary people, which promote the rapid development of advanced diagnostic and therapeutic techniques. Fluorescence, with the advantages of real-time imaging, high sensitivity, superb spatial and temporal resolution, and simple operation, has been employed for the development of novel diagnostic and therapeutic techniques [1, 2]. Most conventional fluorescent materials suffer from the aggregation-caused quenching (ACQ) effect, with bright emission in their dilute solutions, but weak or completely quenched fluorescence at high concentrations or in the aggregated state [3]. To avoid ACQ from taking effect, conventional fluorescent materials are mostly utilized at low concentrations, which introduce the problems of easy photobleaching, low imaging contrast, and unsatisfying therapeutic performance, and greatly hamper their widespread application in the biomedical field.

Materials with aggregation-induced emission (AIE) characteristics perfectly overcome these problems caused by the ACQ effect [3]. Since the concept of “aggregation-induced emission” was first coined by Tang in 2001 [4], investigations on AIE have been a hot topic in various research fields. Luminogens, with AIE attributes (AIEgens), exhibit no or weak emission in solutions, and intense fluorescence in the aggregated state. Thus, they break the fetters that traditional luminescent materials with ACQ properties encounter, solve the problems that bright emissions of luminogens in dilute solutions face such as weakened or quenched when the luminogens are concentrated or aggregated, and extend the real-world application of fluorescent materials in energy, health, and environment [5]. The past two decades have witnessed the blooming development of AIEgens in biological science and biomedical applications due to their unique merits of anti-quenching, high brightness, excellent photostability, fluorescence turn-on fashion, and large Stokes shift [6, 7, 8, 9]. These enthusiastic research efforts have resulted in many novel AIEgens with varied biomedical applications, which can be classified into three aspects of biosensor [10], bioimaging [11, 12] and biomedicine [13].

1.1 AIEgen-based biosensor

Many diseases are accompanied with abnormal activities and concentrations of biomarkers or biomolecules, such as nucleic acids [14], enzymes [15], metal ions [16] and bio-thiols [17]. Fluorescent biosensors are powerful analytical tools for these biological targets. Development of sensitive and selective fluorescent biosensors is of great importance, which may contribute to the early diagnosis and effective treatment of diseases. Thus, a large variety of luminogens, such as fluorescent proteins, organic dyes, and quantum dots [18, 19, 20], have been developed and utilized for sensing the quantity or activity of biological targets. In sensory applications, changes in fluorescence intensity, wavelength, or lifetime of the sensors, upon interacting with targets are the key outputs. Conventional luminogens with their rigid and coplanar molecular structures are emissive in solutions, which may result in high background fluorescence with low sensitivity, and add to the difficulty for sensor designs. In contrast, the novel AIEgens exhibit great practical benefits in sensory applications, which permit the use of dye solutions at any concentration for bioassays and enable the development of fluorescence ‘‘turn-on” biosensors by taking advantage of luminogen aggregation processes [21]. The fluorescence ‘‘turn-on” feature of AIE biosensors offers higher sensitivity and better accuracy over ACQ biosensors. Thus, a lot of outstanding AIE-active biosensors have been constructed for the detection of biomolecules and biomacromolecules, such as amino acid [22], glucose [23], ATP [24], nucleic acid [25], protease [26], and disease-related proteins [27], with the features of high sensitivity, fast response, high signal-to-noise ratio, and extremely low background fluorescence.

AIEgen-based fluorescent biosensors are commonly composed of AIE-active fluorophores and functional units. Tetraphenylethene (TPE) and tetraphenylsilole (TPS), and their modified derivatives account for a substantial portion of the fluorophores in AIE-active biosensors [28]. In sensors, the functional units play an important role in interacting with biological targets [29, 30]. Biomacromolecules, such as nucleic acids and proteins, possess excellent biocompatibility and outstanding specificity, and are frequently used as the functional units [31]. The combination of biomacromolecules and AIEgens not only endows the biosensors with high specificity but also improves the biological activity and water solubility of the probe for accurate and efficient biosensing. In the chapter, Modular Nucleic Acid-Functionalized AIEgen Probes for Biosensing Applications, we will introduce the design mechanism of modular nucleic acid-functionalized AIEgen probes (MNAPs) and their biosensing applications. In the chapter, Peptide-AIEgen Conjugates for Biomedical Diagnosis and Bioimaging, we will discuss the design of AIEgens with various kinds of peptide modifications and their applications in biomedical diagnosis and bioimaging.

AIE-active sensors can also be constructed by taking advantages of their state transition process – when interacting with specific targets, the fluorescence of AIE-active sensors can be turned on upon switching AIEgens from the dispersive state to the aggregated state. Another widely used strategy for sensing with AIEgens is based on exploiting the reactions between the functional groups and the targets to realize the fluorescence turn-on process. In the chapter, The Application of Click Chemistry in the Design of Aggregation-Induced Emission Luminogens for Activity-Based Sensing, we will expound AIEgen-active sensors based on the mechanism of click chemi...