Protein glycosylation has received increased attention for its critical role in cell biology and diseases. Developing new methodologies to discern phenotype-dependent glycosylation will not only elucidate the mechanistic aspects of cell signaling cascades but also accelerate biomarker discovery for disease diagnosis or prognosis. In the analytical pipeline, enrichment at either the protein or peptide level is the most critical prerequisite for analyzing heterogeneous glycan composition, linkage, site occupancy and carrier proteins. Because the critical factor for choosing a suitable enrichment method is primarily a particular technique's selectivity and affinity towards target glycoproteins/glycopeptides, it is important to fully understand the working principles for the different approaches. For mechanistic insight into the enrichment protocol, we focused on the fundamental chemical and physical processes for the commonly used approaches based on: (a) glycan/peptide physicochemical properties (hydrophilic interactions, chelation/coordination chemistry) and (b) glycan-specific recognition (lectin-based affinity, covalent bond formation by hydrazide/boronic acid). Various interaction modes, such as hydrogen bonding, van der Waals interaction, multivalency, and metal- or water-mediated stabilization, are discussed in detail. In addition, we will review the design of and modifications to such methods, hyphenated approaches, and glycoproteomic applications. Finally, we will outline challenges to existing strategies and offer novel proposals for glycoproteome enrichment.

The overpotential (η) of the OER and ORR process over bare and hydroxylated catalysts.

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The analysis of protein glycosylation is important for biomedical and biopharmaceutical research. Recent advances in LC-MS analysis have enabled the identification of glycosylation sites, the characterisation of glycan structures and the identification and quantification of glycoproteins and glycopeptides. However, this type of analysis remains challenging due to the low abundance of glycopeptides in complex protein digests, the microheterogeneity at glycosylation sites, ion suppression effects and the competition for ionisation by co-eluting peptides. Specific sample preparation is necessary for comprehensive and site-specific glycosylation analyses using MS. Therefore, researchers continue to pursue new columns to broaden their applications. The current manuscript covers recent literature published from 2008 to 2013. The stationary phases containing various chemical bonding methods or ligands immobilisation strategies on solid supports that selectively enrich N-linked or sialylated N-glycopeptides are categorised with either physical or chemical modes of binding. These categories include lectin affinity, hydrophilic interactions, boronate affinity, titanium dioxide affinity, hydrazide chemistry and other separation techniques. This review should aid in better understanding the syntheses and physicochemical properties of each type of stationary phases for enriching glycoproteins and glycopeptides.

Graphene-based heterostructure composite is a new type of advanced sensing material that includes composites of graphene with noble metals/ metal oxides/metal sulfides/polymers and organic ligands. Exerting the synergistic effect of graphene and noble metals/metal oxides/metal sulfides/polymers and organic ligands is a new way to design advanced gas sensors for nitrogen-containing gas species including NH 3 and NO 2 to solve the problems such as poor stability, high working temperature, poor recovery, and poor selectivity. Different fabrication methods of graphenebased heterostructure composite are extensively studied, enabling massive progress in developing chemiresistive-type sensors for detecting the nitrogen-containing gas species. With the components of noble metals/ metal oxides/metal sulfides/polymers and organic ligands which are composited with graphene, each material has its attractive and unique electrical properties. Consequently, the corresponding composite formed with graphene has different sensing characteristics. Furthermore, working ambient gas and response type can affect gas-sensitive characteristic parameters of graphene-based heterostructure composite sensing materials. Moreover, it requires particular attention in studying gas sensing mechanism of graphene-based heterostructure composite sensing materials for nitrogen-containing gas species. This review focuses on related scientific issues such as material synthesis methods, sensing performance, and gas sensing mechanism to discuss the technical challenges and several perspectives.

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