Surface plasmon resonance imaging for affinity-based biosensors

SPR imaging (SPRi) is at the forefront of optical label-free and real-time detection. It offers the possibility of monitoring hundreds of biological interactions simultaneously and from the binding profiles, allows the estimation of the kinetic parameters of the interactions between the immobilised probes and the ligands in solution. We review the current state of development of SPRi technology and its application including commercially available SPRi instruments. Attention is also given to surface chemistries for biochip functionalisation and suitable approaches to improve sensitivity

A LysLysLys-tag as trigger in polynorepinephrine epitope imprinting: The case study of soluble PD-L1 detection in serum by optical-based sensing

Polycatecholamines (pCAs)-based molecularly imprinted polymers (MIPs) represent the new performing generation of biocompatible ligand/receptor mimetics. In this context, dealing with MIPs synthesis for bio-macromolecules detection/extraction, one of the critical steps in ensuring effective binding affinity for the parent molecule is the selection of suitable epitopes for pCAs imprinting. To address this challenge, here we investigated the ability of lysine (K) residues to trigger the epitope imprinting process into a polynorepinephrine (PNE) matrix. To this aim, we first designed a set of model epitopes composed of three K and six alanine (A) residues to investigate the influence of each 'KA' combination on the imprinting process and the resulting binding performance by Surface Plasmon Resonance (SPR). Only the case of three flanking K residues in N-terminus arose as an excellent trigger for epitope imprinting. The efficacy of the 3K-tag strategy was then evaluated on two peptide templates belonging to soluble programmed cell death protein 1 ligand (PD-L1), which is of great interest as a cancer biomarker in liquid biopsies. These templates were selected due to their negligible natural ability to be imprinted into the PNE matrix and were modified with 3K-tags, in N-, C-, and N/C- positions, respectively. The SPR sensor developed by exploiting the N-3K tag strategy allowed us to achieve excellent sensitivity (0.31 ± 0.04 ng mL-1) and repeatability (avCV% = 4.5) in human serum samples. This strategy opens new insights both for epitopes' design for pCAs-based mimetics and as triggering tags when native epitopes display negligible imprinting capabilities

Structurally Constrained MUC1-Tn Mimetic Antigen as Template for Molecularly Imprinted Polymers (MIPs): A Promising Tool for Cancer Diagnostics

Abnormal glycoconjugates have distinctly been recognized as potential biomarkers for cancer diagnosis. A great deal of attention has been focused on Tn antigen, an oversimplified mucin-1 O-glycan, over-expressed in different cancers. Herein, we investigate the possibility to replace the use of anti-Tn monoclonal antibodies with an innovative class of catecholamine-based Molecularly Imprinted Polymers (MIPs), emerging in recent years as promising tools for bioanalytical applications. MIPs are synthetic receptors characterized by high sensitivity and specificity towards the imprinted target. Here, original polynorepinephrine-based MIPs coupled to Surface Plasmon Resonance biosensing for Tn antigen recognition are reported. We have verified the imprinting and binding capacity of these MIPs towards very small antigenic entities, represented by the natural Tn antigen and the TnThr mimetic 1 (conjugated to BSA or linked to a MUC1 hexapeptide analogue), and compared the biosensor performances with an anti-Tn monoclonal antibody. The results clearly display the effectiveness of the pursued imprinting strategies