Electrogenerated poly(pyrrole-lactosyl) and poly(pyrrole-3'-sialyllactosyl) interfaces: toward the impedimetric detection of lectins

Dispersible Conjugated Polymer Nanoparticles as Biointerface Materials for Label-Free Bacteria Detection

Fast and efficient identification of bacterial pathogens in water and biological fluids is an important issue in medical, food safety, and public health concerns that requires low-cost and efficient sensing strategies. Impedimetric sensors are promising tools for monitoring bacteria detection because of their reliability and ease-of-use. We herein report a study on new biointerface-based amphiphilic poly(3-hexylthiophene)-b-poly(3-triethylene-glycol-thiophene), P3HT-b-P3TEGT, for label-free impedimetric detection of Escherichia coli (E. coli). This biointerface is fabricated by the self-assembly of P3HT-b-P3TEGT into core-shell nanoparticles, which was further decorated with mannose, leading to an easy-to-use solution-processable nanoparticle material for biosensing. The hydrophilic block P3TEGT promotes antifouling and prevents nonspecific interactions, while improving the ionic and electronic transport properties, thus enhancing the electrochemical-sensing capability in aqueous solution. Self-assembly and micelle formation of P3HT-b-P3TEGT were analyzed by 2D-NMR, Fourier transform infrared, dynamic light scattering, contact angle, and microscopy characterizations. Detection of E. coli was characterized and evaluated using electrochemical impedance spectroscopy and optical and scanning electron microscopy techniques. The sensing layer based on the mannose-functionalized P3HT-b-P3TEGT nanoparticles demonstrates targeting ability toward E. coli pili protein with a detection range from 10³ to 10⁷ cfu/mL, and its selectivity was studied with Gram(+) bacteria. Application to real samples was performed by detection of bacteria in tap and the Nile water. The approach developed here shows that water/alcohol-processable-functionalized conjugated polymer nanoparticles are suitable for use as electrode materials, which have potential application in fabrication of a low-cost, label-free impedimetric biosensor for the detection of bacteria in water.

Glycosylated Conductive Polymer: A Multimodal Biointerface for Studying Carbohydrate-Protein Interactions

Carbohydrate-protein interactions occur through glycoproteins, glycolipids, or polysaccharides displayed on the cell surface with lectins. However, studying these interactions is challenging because of the complexity and heterogeneity of the cell surface, the inherent structural complexity of carbohydrates, and the typically weak affinities of the binding reactions between the lectins and monovalent carbohydrates. The lack of chromophores and fluorophores in carbohydrate structures often drives such investigations toward fluorescence labeling techniques, which usually require tedious and complex synthetic work to conjugate fluorescent tags with additional risk of altering the reaction dynamics. Probing these interactions directly on the cell surface is even more difficult since cells could be too fragile for labeling or labile dynamics could be affected by the labeled molecules that may interfere with the cellular activities, resulting in unwanted cell responses. In contrast, label-free biosensors allow real-time monitoring of carbohydrate-protein interactions in their natural states. A prerequisite, though, for this strategy to work is to mimic the coding information on potential interactions of cell surfaces onto different biosensing platforms, while the complementary binding process can be transduced into a useful signal noninvasively. Through carbohydrate self-assembled monolayers and glycopolymer scaffolds, the multivalency of the naturally existing simple and complex carbohydrates can be mimicked and exploited with label-free readouts (e.g., optical, acoustic, mechanical, electrochemical, and electrical sensors), yet such inquiries reflect only limited aspects of complicated biointeraction processes due to the unimodal transduction. In this Account, we illustrate that functionalized glycosylated conductive polymer scaffolds are the ideal multimodal biointerfaces that not only simplify the immobilization process for surface fabrication via electrochemical polymerization but also enable the simultaneous analysis of the binding events with orthogonal electrical, optical, or mass sensing label-free readouts. We established this approach using polyaniline and polythiophene as examples. Two general methods were demonstrated for glycosylated polymer fabrications (i.e., electropolymerization of monomer bearing α-mannoside residues or click chemistry based mannose conjugation to electrochemically preformed quinone fused polymer with potential to introduce different carbohydrate moieties and construct glycan arrays in a similar manner). Their conjugated π system extending over a large number of recurrent monomer units renders them sensitive optoelectronic materials. The carbohydrate-protein interactions on the side chain could disrupt the electrostatic, H-bonding, steric, or van der Waals interactions within or between polymers, leading to a change of conductivity or optical absorption of the conductive polymers. This will allow concurrent interrogation of these interactions with adjoining biological processes and mechanisms in multimodal fashion. Furthermore, the functionalized glycosylated conductive polymers can be designed and synthesized with controlled oxidation states, desired ionic dopants, and the imperative density and orientation of the sugar ligands that enable the assessment of differential receptor binding profiles of carbohydrate-protein interactions with much more detailed information and high accuracy. Finally, the glycosylated biosensing interfaces were successfully validated for their applications in Gram-negative bacterial detection, antibiotic resistance studies, and antimicrobial susceptibility assays, all based on inferring carbohydrate-protein interactions directly on cell surfaces, thus illustrating their potential uses in infectious disease research, clinical diagnostics, and environmental monitoring of harmful pathogens.

Are glycan biosensors an alternative to glycan microarrays?

Complex carbohydrates (glycans) play an important role in nature and study of their interaction with proteins or intact cells can be useful for understanding many physiological and pathological processes. Such interactions have been successfully interrogated in a highly parallel way using glycan microarrays, but this technique has some limitations. Thus, in recent years glycan biosensors in numerous progressive configurations have been developed offering distinct advantages compared to glycan microarrays. Thus, in this review advances achieved in the field of label-free glycan biosensors are discussed.

Nanoscale controlled architecture for development of ultrasensitive lectin biosensors applicable in glycomics

In this Minireview the most advanced patterning protocols and transducing schemes for development of ultrasensitive label-free and label-based lectin biosensors for glycoprofiling of disease markers and some cancerous cells are described. Performance of such lectin biosensors with interfacial properties tuned at a nanoscale are critically compared to the most sensitive immunoassay format of analysis and challenges ahead in the field are discussed. Moreover, key elements for future advances of such devices on the way to enhance robustness and practical applicability of lectin biosensors are revealed.