Different strategies to prepare SAMs of carbohydrate using indirect method.
Self‐assembled monolayers (SAMs) presenting carbohydrates (glycans) have been widely prepared on gold surfaces to mimic the carbohydrate surfaces that are involved in molecular recognition phenomena in living cells. The binding affinity of carbohydrate immbolized on SAM surfaces to various carbohydrate‐binding proteins (such as lectins) can be studied by optical, electrochemical, piezoelectrical and thermal sensing techniques. The lectins present on the surface of pathogens (e.g., bacteria or viruses) can be used as targets for capturing onto carbohydrates immobilized on SAM surfaces. The immobilized carbohydrates can also be used for detecting different types of disease biomarkers present in bodily fluids. Synergistic properties of carbohydrate SAMs and gold nanoparticles can be used for vaccine preparation and drug delivery. By studying different types of glycans, their properties, and the behavior toward recognition of specific pathogens and biomarkers, we can develop not only new therapeutics but also enhance the diagnostic strategies of various diseases. In this chapter, we discuss carbohydrate‐terminated SAMs and their common preparation strategies. Next, we focus on roles of different components of SAMs, characterization techniques, and applications.
- self‐assembled monolayers (SAMs)
- gold surface
- click reaction
- carbohydrate‐lectin interaction
- E‐coli detection
Carbohydrates are biological molecules, present widely in nature in diverse forms and have varieties of functions . Their role in living organisms is indispensable, whether it is as a structural support (e.g., cellulose and chitin), in energy storage (e.g., glycogen and starch), in the immune system, or for fertilization and development [2, 3]. The glycans are the carbohydrate parts of glycoconjugates, such as glycoproteins, glycolipids, or proteoglycans, and their importance in human health and disease is an ever expanding field . A major part of the field concerns the study of the organization of carbohydrates at interfaces and their interaction with carbohydrate‐binding proteins. Self‐assembled monolayers (SAMs) of carbohydrate‐terminated alkanethiols and of other carbohydrate derivatives conjugated to species pre‐immobilized on gold such as branched polymers and dendrimers have served as model systems in many studies of these interactions and in the development of biosensors based on carbohydrate recognition [4, 5]. These SAMs have been formed both by direct immobilization of carbohydrate‐terminated alkanethiols and by conjugation of glycans to pre‐formed SAMs with reactive terminal groups . The complexity of the carbohydrates immobilized range from monosaccharides to complex oligosaccharides of varied biological functions. Central to these studies is the goal of understanding the structure and organization of the SAMs, and this has been approached using a range of methods, including surface analysis, surface spectroscopy, scanning probe microscopy, and electrochemical methods. The binding of proteins to these SAMs has been followed using methods, including surface plasmon resonance (SPR), impedance spectroscopy, and quartz crystal microbalance (QCM). In this chapter, we will seek to review the literature concerning SAMs containing terminal carbohydrates, their fabrication by direct or indirect coupling methods, and their structural characterization. The applications of these SAMs in protein‐binding studies and biosensor development will also be discussed.
2. Self‐assembled monolayers
Organic molecules having functional head‐groups (e.g., thiols, disulfides, and amines) and tail groups at the end of hydrophobic chains (e.g., alkanes and polyethylene glycols) can easily self‐assemble on noble metal surfaces lowering the free energy at the interface to form densely packed monolayer films, called self‐assembled monolayers (SAMs) . Different types of functional groups can be attached to the terminal end of the hydrophobic part depending on the nature of the study, through which further chemistry can be performed linking fields of the material chemistry and organic/biochemistry. SAMs of organosulfur compounds are the most‐studied SAMs to date because of strong thiol‐gold bond formation [8, 9]. A schematic diagram of an ideal alkanethiol SAM immobilized on gold surfaces having terminal functional groups is shown in Figure 1
One of the common methods of preparing SAMs of organosulfur derivatives is by immersing a metal substrate into dilute (1–10 mM) ethanolic solution of the desired organosulfur compound for 12–24 h under ambient conditions . When sulfur atoms come in contact with a clean metal surface, they start forming monolayers instantly; however, the molecules reorganize themselves if left in the solution over a longer period, minimizing the density of defects . Alkyl chains of SAMs arrange themselves in trans‐conformation with nearly 20–30° tilt from normal to the metal surface . However, studies have shown that overall arrangement and binding of SAMs on gold surfaces depend on numbers of factors, including length of alkyl chains, the nature and distance between terminal functional groups, concentration and purity of adsorbate, immersion time, and substrate morphology .
3. Preparation of SAMs having terminal carbohydrates
Preparation of microarrays of carbohydrates to mimic the cell surface for the in vitro study of their interactions with pathogens or other biological molecules is very important. Microarrays present a surface onto which pathogens can undergo multivalent attachment amplifying the relative affinities as on cell surfaces and above that of a single ligand. The pathogens or biological molecules captured on the array can also be easily harvested and further tested. There are different methods to prepare arrays of carbohydrates on solid surfaces; one of the popular methods is through SAMs formation. Here, we will be specifically focusing on the SAM of carbohydrates prepared on a gold substrate through organosulfur molecules. The two common approaches (Figure 2) for forming SAMs of carbohydrates on gold surfaces are, (1) direct method: The carbohydrate molecules of interest are modified with the organosulfur molecule first, followed by direct SAMs formation on the gold surface; and (2) indirect method: The SAM of organosulfur molecule having a suitable terminal functional group is prepared on the gold surface first, followed by a reaction to conjugate it to the carbohydrate of interest.
3.1. Indirect methods
The indirect method of forming carbohydrate SAMs does not require preparation of organosulfur molecules already linked to the carbohydrate of interest. The strategy also avoids the possibility that the prepared molecules may decompose or oxidize by the time they are used and might not form stable SAMs. An advantage of the indirect SAM formation method is that each step can be tracked in situ , which can be imagined as building a tower by stacking bricks on top of one another with cement between the bricks, whereas the direct method is like transferring a whole tower in one piece. Use of indirect methods for the preparation of carbohydrate SAMs date back to the 1990s. In 1995, Lofas used a step‐by‐step method to form SAMs containing dextran, a hydrophilic linear polymer based on 1,6‐linked glucose units, on a gold surface . As a first step, a SAM of 16‐mercaptohexadecan‐1‐ol was formed on a gold surface, followed by the reaction of the exposed hydroxyl groups with epichlorohydrin to prepare terminal epoxy groups. The epoxy group was found to capture the dextran randomly under basic conditions. The immobilized dextran was subsequently reacted with bromoacetic acid to introduce terminal functional carboxylic groups, which were in turn activated using a mixture of N‐ethyl‐N'‐dimethylaminopropyl‐carbodiimide and N‐hydroxysuccinimide to capture monoclonal antibodies (MAbs). Three different types of MAbs were then tested against their antigen, HIV protein p24. The as‐prepared sensor was sensitive enough to distinguish differences in the affinity of the three MAbs toward p24 . During the two decades since, different types of strategies have been discovered for preparing SAMs of carbohydrates using indirect methods, applicable for immobilizing both simple and complex carbohydrate molecules.
Click chemistry‐based reactions are popular indirect methods for formation of carbohydrate SAMs. Click reactions skip the tremendous synthetic efforts required for the preparation of thiolated carbohydrates to be used for direct SAM formation. In addition, this reaction can tolerate a wide variety of functional groups and can be performed over a broad range of temperature and pH with minimal by‐product formation [15, 16].
One of the early uses of click reaction for the carbohydrate SAM formation on a gold surface was performed by Houseman and Mrksich in 2002. They used Diels‐Alder reaction to connect benzoquinone‐terminated SAM surfaces to different common monosaccharides derivatized with cyclopentadiene and prepared carbochips . The carbochips were then utilized for profiling lectin‐binding specificity to their corresponding monosaccharides using SPR and confocal fluorescence microscopy as shown in Figure 3. The same group soon reported another click reaction strategy based on maleimide‐thiol chemistry for preparing SAMs of carbohydrates . They synthesized four different monosaccharides (mannose, galactose, glucose, and N‐acetylglucosamine) having thiol groups at the anomeric centers, which reacted selectively with the terminal maleimide groups of pre‐immobilized SAMs on gold surfaces to present carbohydrate‐terminated SAMs. They then prepared a carbohydrate array to study the specificity of these carbohydrates to their corresponding lectins using confocal fluorescence microscopy, as before. This strategy of maleimide‐thiol reaction can be used for preparing carbohydrate array SAMs having terminal mannoses and interrogate GFP‐transfected
The most commonly used click reaction for preparing carbohydrates SAMs, however, is the Cu(I)‐catalyzed Huisgen 1, 3‐dipolar cycloaddition or the copper(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC) reaction . The first step in this method is to form an organosulfur SAM having either alkyne or azide terminal groups [20, 21]. If the alkyne group is presented at the SAM's surface, it reacts with azide groups available on anomeric positions of carbohydrate molecules of interest and vice versa . This click reaction results in formation of a 1,2,3‐triazole ring with the SAM presenting the terminal carbohydrate . Zhang and coworkers used this chemistry to immobilize azido sugars—mannose, lactose, and α‐Gal trisaccharides—and studied their interactions with their corresponding specific lectins . Using QCM, the apparent affinity constant (
To create a well‐defined multivalency, SAMs of glycodendrimers of various generations were prepared using CuAAC reactions on a gold surface (Figure 4) and characterized using XPS, ellipsometry, MALDI‐ToF mass spectrometry, cyclic voltammetry, 1H and 13C NMR, contact angle goniometry and FTIR [4, 26]. The equilibrium association constants (
Recently, the CuAAC along with amine/isothiocyanate click reactions were used by Grabosch and coworkers to prepare mannosylated SAMs on gold surfaces . The surface was then used for selective recognition of GFP‐transformed
3.2. Direct method
The indirect method of forming SAM of carbohydrates has some advantages, but the direct method has also been widely used within last two decades. In this method, the carbohydrate (or glycan) of interest is directly functionalized with an organosulfur molecule, and the synthetic product is characterized and confirmed before forming SAMs. In the next step, freshly cleaned gold surface is incubated on ethanolic solution of the functionalized molecule for 1–24 h at ambient conditions to prepare the SAM. This method avoids multistep surface reactions. In 1996, Fritz and coworkers reported SAMs of a hexasaccharide molecule functionalized with alkanethiols on gold surfaces . The conditions for high‐density SAM formation were explored by performing experiments with or without protecting the hydroxyl groups with acetyl groups and determining whether unprotecting it after or before the immobilization gave the optimal condition. The optimal condition was found to be adsorption of the unprotected molecules from solution. The Russell laboratory later synthesized mannose‐terminated alkanethiols to prepare SAMs and selectively capture Con A, and the expected selective capture of Con A was determined using reflection absorption infrared spectroscopy (RAIRS) and surface plasmon resonance (SPR); l‐fucose‐specific lectin
4. Types of terminal carbohydrates
It is possible to immobilize or form microarrays of a wide variety of carbohydrates on gold surfaces using SAM techniques. Different types of monosaccharides [17, 21, 27, 35–46], disaccharides [42, 43, 47–50], oligosaccharides [45, 46, 49–54], polysaccharides , and dendrimers [4, 5, 26] can be immobilized as a terminal functional group of the SAM depending on the nature of the study. Table 2 lists some of the carbohydrates used as terminal functional groups of the SAM and their applications. The detailed applications of the carbohydrates will be discussed later.
5. Role of linkers and mixed SAMs
The spacer connecting the sulfur atom to the terminal carbohydrates has an important role in the arrangement and application of SAMs. The most commonly used linkers are repeating units of a methylene group (‐CH2), ethylene glycol (‐OCH2CH2) and the combination of both . However, linkers can also be made from aromatic compounds , dendrimers [4, 5], and peptides . Connecting the different types of linkers previously present on the thiols or carbohydrates may introduce complex structures to the linker; for example, triazoles from alkyne/azides reaction, thiourea‐bridge from isothiocyanide/amine reaction and amides from N‐hydroxyester/amine reaction. The main goals of the linkers are to provide strong support to the terminal group with a proper orientation, keep the terminal group far from the substrate, and resist non‐specific interactions with proteins.
It has been reported that due to kinetic and thermodynamic reasons, longer chain linkers are relatively ordered and robust . The length of the linker is also important for the arrangement of the SAM, which can significantly change the orientation of SAM as shown by Yatawara and coworkers . Alkanethiol linkers of terminal glucose having 11 and 16 carbons chain have similar orientations, but are totally different compared to a cysteine containing linker. A study comparing the effect of thioctic acid amide and alkanethiol linkers on the interactions of terminal mannoses with specifically binding lectin Con A, non‐specific lectins and with the highly adsorbent “sticky” proteins, fibrinogen and cytochrome c was performed . The results show that the thioctic acid amide‐based linker was better at resisting the nonspecific interactions while specifically binding terminal mannose to its corresponding lectin. It was claimed that this linker can resist adsorption of fibrinogen and cytochrome c better than ethylene oxide‐based SAMs.
Even though the longer chain linkers are preferred due to various advantages, monolayers of oligosaccharides (e.g., hyaluronan, chitohexaose, and chitosan hexamer) have been successfully immobilized on gold by modifying the reducing ends of the carbohydrates with thiosemicarbazide (TSC) (Figure 6) [53, 58, 59]. The immobilized oligosaccharides SAMs were then used for specifically capturing different types of cell to be used in cell culture applications [53, 59, 60].
Mixed SAMs of carbohydrates are generally formed by two different constituents of thiolated molecules, one having terminal carbohydrates and other lacking carbohydrate molecules. The most common way of making mixed SAMs of carbohydrates on gold surfaces is by co‐adsorption of the two components from solution . Other methods to prepare mixed SAMs are by adsorption of asymmetric disulfides on gold surfaces  and by ligand exchange reaction . In the ligand exchange reaction, new thiolated molecules are introduced on the surface of the already formed SAMs by a thiol‐for‐thiol mechanism . However, newly introduced molecules may not yield homogeneously mixed SAMs. The relative ratio of the component of the mixed SAM on the surface depends on the mole ratio of the components in the solution. However, increasing mole ratio of one component in solution does not necessarily increase its ratio on surface in a directly proportional manner .
A main goal of making a mixed SAM is to minimize non‐specific interactions and create a biorepulsive background, as the hydrophobic chain of the linker might not be able to resist non‐specific interactions. Mixed SAMs are also prepared to control the density of the terminal carbohydrates, as it has been found that crowding of receptors on the substrate surface is not an optimal condition for the binding of proteins or other analytes . The crowded receptors may interact with each other or hinder the binding of the approaching analyte to the nearby receptors.
Mixed SAMs having two different types of terminal carbohydrates can also be created for a dual function. Aykac¸ and coworkers prepared SAMs of two different carbohydrates, lactose and β‐cyclodextrin, on gold nanoparticles to selectively detect human galectin‐3 through lactose whereas at the same time loading anticancer drug methotrexate on β‐cyclodextrin . This synergistic effect of two different terminal carbohydrates was found to be very effective for site‐specific delivery of anticancer drug than when they are used individually.
6. Types of head‐group
SAMs of carbohydrates on gold surfaces are extensively prepared based on thiol or disulfide head-groups. Thiols have higher solubility and normally form a well‐ordered surface compared to disulfides . However, they are susceptible to oxidation, forming sulfonates or disulfides and degrade over the time . Disulfides, being the less soluble component, may precipitate out forming multilayer contamination if not prepared carefully . In spite of this, disulfides are frequently used as head‐groups for carbohydrate‐terminated SAMs . The carbohydrate‐terminated SAMs formed by using dialkyl disulfide groups are found to be indistinguishable from those formed from the corresponding thiol and are believed to be formed by the cleavage of disulfide bond [66, 67]. However, such phenomenon is not very well studied or understood for the disulfides present in the cyclic form such as in the case of lipoic acid‐based linkers. To reduce the problem of oxidation of thiols, they can be protected using different strategies and reduced in situ just before SAM formation. This can be done by keeping them as disulfides before and reducing them to corresponding thiols using dithiothreitol  or by first protecting the thiols using the S‐trityl group followed by de‐tritylation using trifluoroacetic acid and triethylsilane in dichloromethane .
7. Gold substrates for SAMs formation
Gold substrates are so far the most used and studied substrate for the formation of carbohydrate SAMs not only because they are capable of supporting stable SAMs due to Au‐S bonding but also due to their conductivity, chemical and physical stability, and biocompatibility. SAMs of carbohydrates can be prepared on gold surfaces having different morphologies, such as planar (e.g., bulk or thin‐films) to nanostructured surfaces (e.g., nanoparticles, nanostructured films, and nanoporous structures). Nanostructures of gold are intriguing to scientists because they can strongly scatter and absorb light due to large optical field enhancements  and have a high surface area‐to‐volume ratio  while still maintaining their other important bulk properties. Because of these properties, nanostructures of gold have application in diverse fields, including biomedicine (drug delivery), energy (hydrogen storage, solar cell, and battery), optics (sensors), and electronics (computer chips, information storage) [69, 71]. Carbohydrates SAM on nanoparticles can be prepared using direct and indirect methods similar to those explained before. However, they can also be prepared; at the same time, gold nanoparticles are prepared using reduction of gold salts by keeping the desired thiolated carbohydrates in the same solution mixture. The ligand exchange reaction is another way to introduce the SAM of desired carbohydrates to the already formed carbohydrate SAMs on nanoparticles surfaces . SAMs prepared on nanoparticles may not be exactly same as the SAMs prepared on a planar surface due to the high radius of curvature of nanoparticles . Since the carbohydrate immobilized nanoparticles are free to move around, they are used for studying the self‐recognition of different carbohydrates , as possible inhibitors of lung cancer metastasis  and as an antitumor agent [41, 73]. SAMs of carbohydrates are also immobilized on other robust nanostructures of gold such as nanostructured gold film  and nanoporous gold (np‐Au), which can be used as a biosensor transducer . np‐Au is a three‐dimensional structure having pores (inter‐ligament gaps) and ligaments with widths on the order of a few nanometers to a few hundreds of nanometers [70, 76]. np‐Au was also used as a solid support for synthesizing disaccharides and trisaccharides starting from simple monosaccharide‐terminated SAMs [77, 78].
8. Characterization techniques
There are wide varieties of methods to characterize the successful formation of SAM having terminated carbohydrates on gold surfaces and to study their interaction with other biomolecules. However, there is no single technique that alone can characterize the carbohydrates SAMs and their interactions completely, so different techniques should be used to support the result obtained from one method. Based on the purpose of the study, some of the most frequently used techniques are now discussed.
8.1. Surface wettability
The wettability of the surface before and after the modification by carbohydrate‐terminated SAMs can be determined using contact angle goniometry by measuring the contact angle between water droplet and the surface . The contact angle can be calculated by first taking images of the droplet of water on the surface and using software to fit different models. If contact angle is greater than 90°, the surface is considered hydrophobic; and if smaller than 90°, the surface is considered hydrophilic . Unprotected carbohydrate‐terminated surfaces typically create low contact angles owing to their hydrophilic nature. The static contact angle determined using a sessile droplet is the common method to check the surface wettability. However, due to the deviation from an ideal nature of the surface, there is always a contact angle hysteresis ranging from advancing contact angle to the receding contact angle . The Liedberg group compared the wettability of the surface created with methylated and nonmethylated galactose‐terminated SAMs on gold surfaces . It was found that nonmethylated galactose surfaces had contact angle <10° demonstrating its hydrophilic properties, whereas methylated galactose surfaces had contact angle >70° demonstrating relative hydrophobicity. Dietrich and coworkers used contact angle goniometry to measure the contact angle of dimannoside‐terminated SAMs on gold surfaces, which was found to be 36° ± 2° . The reported contact angle is high compared to a pure hydroxyl‐terminated surface, attributed to the exposed hydrophobic aliphatic linker. Fyrner and coworkers measured the advancing contact angle of oligo(lactose)‐based thiol SAMs on gold, and it was found to be <10° . This demonstrates a very hydrophilic surface as expected because of the highly hydroxylated oligosaccharides moieties.
8.2. Thickness and roughness
In a slightly different direction, AFM was also used for controlling the spacing of already immobilized carbohydrate SAMs by increasing the imaging force above the displacement threshold , which was then used to monitor the binding affinity of viral envelope glycoprotein gp120 to SAM of galactosylceramide prepared at controlled edge‐to‐edge gaps. The protein shows better immobilization when edge‐to‐edge separation of SAMs falls between 1.3 and 9.4 nm, with a 4.8 nm gap giving the optimal binding.
8.3. Chemical composition
8.4. Binding affinity
LSPR was applied to study monolayers of colloidal Au nanoparticles supported on glass. These were modified by polymer brushes presenting multiple glucose residues, and LSPR was used to determine a binding constant of 5.0 ± 0.2 × 105 M-1 noted as larger than that for Con A binding to methyl α‐d‐glucopyranoside of 2.4±0.1 × 103 M-1 in solution due to multivalent binding effects . The use of supported gold nanoparticles modified with a polymer brush presenting many mannose units was also applied to follow Con A binding, resulting in an apparent association constant of 7.4 ′ 0.1 × 106 M-1, noted as much greater than that for Con A to methyl α‐d‐mannopyranoside in solution of 7.6±0.2 × 103 M-1, with the difference attributed to multivalent binding . Galactose presenting polymer brushes was also used to modify colloidal gold monolayers and their binding of the lectin RCA120 was followed by LSPR, and the binding of HepG2 cells which contain galactose receptors was followed by optical microscopy . The interaction of wheat germ agglutinin (WGA) with a disulfide‐modified telomer polymer on a colloidal gold monolayer was also followed by LSPR .
The carbohydrates present on the cells surface can act as a receptor for many pathogens to facilitate cell‐cell adhesion through which humans can be infected, for example, mannose binds pathogenic bacteria
9.1. Carbohydrate–lectin interactions
The diverse arrangement of carbohydrate in biological molecules makes their study challenging. However, the ubiquitous presence of 10 common monosaccharaides, namely, d‐glucose (d‐Glc), d‐mannose (d‐Man), d‐galactose (d‐Gal), N‐acetylglucosamine (d‐GlcNAc), N‐acetylgalactosamine (d‐GalNAc), d‐glucuronic acid (d‐GlcA), l‐fucose (l‐Fuc), N‐acetylneuraminic acid (Neu5Ac), d‐xylose (d‐Xyl) and L-iduronic acid (L-IdoA), has made it easier to understand these structures and their functions, mainly by selecting lectins specific to these monosaccharides. Lectins are the proteins having an ability to bind specific types of carbohydrate  and hence to variety of glycoproteins, bacteria, and viruses through their carbohydrate‐binding moieties . Examples of commonly used lectins include Concanavalin A (Con A)‐specific to mannose and glucose , peanut agglutinin (PNA) and jacalin‐specific to galactosyl (β‐1,3) N‐acetylgalactosamine sugar sequence  and wheat germ agglutinin (WGA)‐specific to N‐acetylglucosamine.
Carbohydrate‐lectin interactions can be studied in solution using techniques like isothermal titration calorimetry  or on gold surfaces using SPR, LSPR, EIS, and QCM [75, 104]. It has been found that the interactions between carbohydrate and lectin are stronger when performed on solid surfaces. The reason behind this is the favorable multivalency condition on the solid surface . However, care should be taken when studying the interactions on solid surface as the defects on immobilized film can cause the analyte (protein) to immobilize directly on solid surface and can also precipitate the protein. The main goal of the carbohydrate‐protein interactions study is to find the binding constant or to detect protein at low concentration. The change in response before and after the interactions of carbohydrate and lectin mostly in the form of optical, electrochemical, thermal or mass response is recorded. Then the change in response is recorded for wide range of concentrations creating a calibration plot, from which binding kinetics can be determined. The lower the value of
Since monosaccharides are easier to be derivatized to prepare SAMs, their interactions with their corresponding lectins have been well explored using different techniques. For example,
9.2. SAMs of carbohydrates for the detection of
Understanding the microbial force of adhesion to the carbohydrate surface can help develop a new approach for detection and prevention of bacterial infection by blocking or decreasing the adhesion capacity. The forces of adhesion of UPEC to the mannose presenting SAM surface, representing the surface of epithelial cells, have been studied using optical tweezers by Whitesides group . The group was successful to orient the bacteria end‐on on mannose surface, from where they can be immediately detached and reattached onto mannose surface and the force required to detach from the surface was measured. In another study, SAMs of octadecanethiol on a gold electrode surface and polydiacetylene derivatives with or without terminal mannose were used to prepare bilayer similar to the biological membrane. Incubation of the prepared electrode in
The adhesion of Con A to
SAMs of carbohydrate can be prepared on gold surfaces to present multivalency and mimic the cell surface to study different physiologically significant interaction in vitro. In this chapter, we have presented the direct and indirect methods for forming SAM of carbohydrates on gold surfaces. Common strategies of preparing SAMs using indirect method are discussed and presented. We have also tabulated some of the commonly used carbohydrate terminal groups of the SAM, and their applications are presented. Different characterization techniques based on nature of study were also presented. Finally, the application of carbohydrates SAM for lectin and bacteria detection has been discussed.
The authors acknowledge recent support of their work in this area by University of Missouri–St. Louis and by the NIGMS awards R01‐GM090254 and R01‐GM111835.