No abstract

Ultrasensitive impedimetric lectin biosensors recognising different glycan entities on serum glycoproteins were constructed. Lectins were immobilised on novel mixed self-assembled monolayer containing 11-mercaptoundecanoic acid for covalent immobilisation of lectins and betaine terminated thiol to resist non-specific interactions. Construction of biosensors based on Concanavalin A (Con A), Sambucus nigra agglutinin type I (SNA) and Ricinus communis agglutinin (RCA) on polycrystalline gold electrodes was optimised and characterised with a battery of tools including electrochemical impedance spectroscopy, various electrochemical techniques, QCM, FTIR spectroscopy, AFM, XPS and compared with a protein/lectin microarray. The lectin biosensors were able to detect glycoproteins from 1 fM (Con A), 10 fM (RCA) or 100 fM (SNA) with a linear range spanning 6 (SNA), 7 (RCA) or 8 (Con A) orders of magnitude. Furthermore, a detection limit for the Con A biosensor down to 1 aM was achieved in a sandwich configuration. A non-specific binding of proteins for the Con A biosensor was only 6.1% (probed with an oxidised invertase) of the signal towards its analyte invertase and a negligible non-specific interaction of the Con A biosensor was observed in diluted human sera (1000x), as well. The performance of the lectin biosensors was finally tested by glycoprofiling of human serum samples from healthy individuals and those having rheumatoid arthritis, which resulted in distinct glycan pattern between these two groups.

Electrochemical techniques have great promise for low-cost miniaturised easy-to-use portable devices for a wide range of applications–in particular, medical diagnosis and environmental monitoring. Different techniques can be used for biosensing, with amperometric devices taking the central role due to their widespread application in glucose monitoring. In fact, glucose biosensing takes an approximately 70% share of the biosensor market due to the need for diabetic patients to monitor their sugar levels several times a day, making it an appealing commercial market.In this review, we present the basic principles of electrochemical biosensor devices. A description of the different generations of glucose sensors is used to describe in some detail the operation of amperometric sensors and how the introduction of mediators can enhance the performance of the sensors. Electrochemical impedance spectroscopy is a technique being increasingly used in devices due to its ability to detect variations in resistance and capacitance upon binding events. Novel advances in electrochemical sensors, due to the use of nanomaterials such as carbon nanotubes and graphene, are presented as well as future directions that the field is taking.