Detection Of Cell Surface Proteins Research Articles

Identification of senescent cell subpopulations by CITE-seq analysis.

Cellular senescence, a state of persistent growth arrest, is closely associated with aging and age-related diseases. Deciphering the heterogeneity within senescent cell populations and identifying therapeutic targets are paramount for mitigating senescence-associated pathologies. In this study, proteins on the surface of cells rendered senescent by replicative exhaustion and by exposure to ionizing radiation (IR) were identified using mass spectrometry analysis, and a subset of them was further studied using single-cell CITE-seq (Cellular Indexing of Transcriptomes and Epitopes by Sequencing) analysis. Based on the presence of proteins on the cell surface, we identified two distinct IR-induced senescent cell populations: one characterized by high levels of CD109 and CD112 (cluster 3), the other characterized by high levels of CD112, CD26, CD73, HLA-ABC, CD54, CD49A, and CD44 (cluster 0). We further found that cluster 0 represented proliferating and senescent cells in the G1 phase of the division cycle, and CITE-seq detection of cell surface proteins selectively discerned those in the senescence group. Our study highlights the heterogeneity of senescent cells and underscores the value of cell surface proteins as tools for distinguishing senescent cell programs and subclasses, paving the way for targeted therapeutic strategies in disorders exacerbated by senescence.

Intracellular metal enhanced fluorescence utilizing gold nanoparticles embedded in hydrogel droplets for sensitive protein detection in cells

Cellular protein detection is necessary for monitoring various biological pathways associated with complex diseases such as cancer. Detecting intracellular proteins is more challenging than cell surface protein detection because most antibodies cannot freely cross the cellular membrane. Cellular membrane permeabilization is thus required to facilitate the antibody diffusion and achieve adequate detection when combined with various conventional protein detection methods (e.g., flow cytometry and immunocytochemistry). However, these methods come with sensitivity challenges when a large number of cells are unavailable. Therefore, for early disease diagnostics and prognosis, novel methods are needed to achieve higher sensitivity to track disease-related proteins from small amounts of cells at early stages of disease progression. Here we applied a novel biosensing platform that co-entraps cells and gold nanoparticles in 3D hydrogel droplets to achieve sensitive fluorescence-based detection and quantification of intracellular proteins in intact cells. Importantly, intracellular metal enhanced fluorescence (iMEF) was achieved using gold nanoparticles via cell permeabilization. The intracellular gold-nanoparticles, together with the high cell loading capacity of the hydrogel droplets, enhanced the fluorescence signals and in turn improved assay sensitivity compared to conventional methods. After assay optimization, we demonstrated the detection of Heat Shock Protein 70, a common cancer marker, with as little as 250 cells. This technology was also able to distinguish between cancerous and non-cancerous samples when mimicking a clinical fine needle aspiration procedure. Compared to conventional assays measuring the same protein, the assay sensitivity was improved by two to three orders of magnitude, allowing for highly sensitive intracellular protein detection from minimal amounts of cells.

Gold Nanowires Array-Based Closed Bipolar Nanoelectrode System for Electrochemiluminescence Detection of α-Fetoprotein on Cell Surface.

Inspired by the promising applications of a closed bipolar electrodes (c-BPEs) system in electrochemiluminescence (ECL) detection of cell adhesion and disease-related biomarkers, here, a gold nanowires array-based c-BPEs system was constructed for cell surface protein detection. Regular and uniform gold nanowires array were prepared by intermittent potentiostatic deposition. Then, two poly(dimethylsiloxane) (PDMS) chips with a hole diameter of 2 mm as a reservoir were placed at both sides of Au nanowires array to construct c-BPEs system. Thionine-functionalized silicon dioxide nanoparticles conjugated to antibody (Ab2-Th@SiO2) were used as the electrochemical probe, while [Ru(bpy)3]2+-wrapped SiO2 nanoparticles (Ru(II)@SiO2) were employed as the ECL signal readout. Taking α-fetoprotein (AFP) as model, the gold nanowires array-based c-BPEs system allowed sensitive detection of AFP at a linear range from 0.002 to 50.0 ng/mL and at least 6 living cells ascribing to the synergetic amplification effect at both sensing and reporting chambers. Besides, the amount of AFP expressed by HepG2 cells was calculated to be 6.71 pg/cell. The presented strategy with high sensitivity provided a promising and universal platform for the detection of other cancer cells and disease-related biomarkers (such as proteins, glycan, miRNA).

Detection and Functional Evaluation of the P2X7 Receptor in hiPSC Derived Neurons and Microglia-Like Cells.

A large body of evidence suggests the involvement of the ATP-gated purinergic receptor P2X7 (P2X7R) in neurodegenerative diseases, including Alzheimer’s disease. While it is well-described to be present and functional on microglia cells contributing to inflammatory responses, some reports suggest a neuronal expression of the receptor as well. Here, we present experimental results showing P2X7 receptors to be expressed on human hiPSC-derived microglia-like cells, hiPSC-derived neuronal progenitors and hiPSC-derived matured neuronal cells. By applying cell surface protein detection assays, we show that P2X7R is not localized on the cell membrane, despite being detected in neuronal cells and thus may not be available for directly mediating neurotoxicity. On hiPSC-derived microglia-like cells, a clear membranous expression was detected. Additionally, we have not observed differences in P2X7R functions between control and familial Alzheimer’s disease patient-derived neuronal cells. Functional assays employing a P2X7R antagonist JNJ 47965567 confirm these findings by showing P2X7R-dependent modulation of microglia-like cells viability upon treatment with P2X7R agonists ATP and BzATP, while the same effect was absent from neuronal cells. Since the majority of P2X7R research was done on rodent models, our work on human hiPSC-derived cells presents a valuable contribution to the field, extending the work on animal models to the human cellular system and toward clinical translation.

Impact of cell harvesting methods on detection of cell surface proteins and apoptotic markers

Assays based on the flow cytometry technique allow a convenient analysis of multiple cellular parameters; however, their results should be interpreted cautiously due to a strong impact of confounding factors. Different techniques in cell culturing such as either enzymatic or mechanic detachment of adherent cells can heavily influence the structure of the cell membrane or presence of the surface antigens leading to strong false positive signals, and finally, substantial experimental bias. The aim of our study was to assess and compare the impact of cell harvesting methods (both enzymatic and non-enzymatic) on the apoptosis process and on the surface antigen cytometric analyses. We found significant differences in the quality of analysis in terms of the amount of detected surface markers determined by the detachment method. Our results demonstrated clearly how important it is to carefully choose the appropriate detachment method and may help to avoid mistakes in experiment planning. In conclusion, we recommend to adjust the detachment method to the type of analyzed markers (surface antigens or translocated phosphatidylserine).

High-Throughput Single-Cell Immunoassay in the Cellular Native Environment Using Online Desalting Dual-Spray Mass Spectrometry.

Single-cell mass spectrometry (MS) remains challenging in the analysis of cells in the native environment due to the severe ion suspension from nonvolatile salts. Synchronous desalting and ionization would be ideal to both ensure the native environment and remove the salt interference. Here, a novel dual-spray ionization technique combining electrospray and nanoelectrospray ionization (ESI-nESI) was developed, enabling highly efficient online desalting during the ionization process. In situ detection of cell surface proteins from the intact cells in phosphate buffer saline (PBS) was achieved by dual ESI-nESI MS with the help of an MS-based immunoassay using rhodamine-based mass tags. These mass tags were confirmed to be highly competitive during desalting, which improved the protein detection sensitivity to a single-cell level. Through the combination of the single-cell immunoassay with ESI-nESI MS, the important surface protein markers, cancer antigen 125, in two cancer cell lines (OVCAR-3 and MCF-7) suspended in the PBS buffers were screened in a high-throughput cytometric mode, along with some proposed cellular endogenous lipids. The ESI-nESI MS system is promising for multidimensional organic mass cytometric analysis in the cellular native environment for clinical use and many basic biology researches.

Riemannian geometry and statistical modeling correct for batch effects and control false discoveries in single-cell surface protein count data.

Recent advances in next generation sequencing-based single-cell technologies have allowed high-throughput quantitative detection of cell-surface proteins along with the transcriptome in individual cells, extending our understanding of the heterogeneity of cell populations in diverse tissues that are in different diseased states or under different experimental conditions. Count data of surface proteins from the cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) technology pose new computational challenges, and there is currently a dearth of rigorous mathematical tools for analyzing the data. This work utilizes concepts and ideas from Riemannian geometry to remove batch effects between samples and develops a statistical framework for distinguishing positive signals from background noise. The strengths of these approaches are demonstrated on two independent CITE-seq data sets in mouse and human.

β-Galactosidase-Catalyzed Fluorescent Reporter Labeling of Living Cells for Sensitive Detection of Cell Surface Antigens.

The ability to detect cell surface proteins using fluorescent-dye-labeled antibodies is crucial for the reliable identification of many cell types. However, the different types of cell surface proteins used to identify cells are currently limited in number because they need to be expressed at high levels to exceed background cellular autofluorescence, especially in the shorter-wavelength region. Herein we report on a new method, quinone methide-based catalyzed labeling for signal amplification (CLAMP), in which the fluorescence signal is amplified by an enzymatic reaction that strongly facilitates the detection of cell surface proteins on living cells. We used β-galactosidase as an amplification enzyme and designed a substrate for it, called MUGF, that contains a fluoromethyl group. Upon removal of the galactosyl group in MUGF by β-galactosidase labeling of the target cell surface proteins, the resulting product containing the quinone methide group was found to be both cell-membrane-permeable and reactive with intracellular nucleophiles, thereby providing fluorescent adducts. Using this method, we successfully detected several cell surface proteins, including programmed death ligand 1 protein, which is difficult to detect using conventional fluorescent-dye-labeled antibodies.

Improved sensitivity in cell surface protein detection by combining chemical labeling with mechanical lysis in a colorectal cancer cell model

To develop a new technique for improved cell surface protein detection and analysis by combining chemical labeling with mild cell lysis using model HCT 116 colorectal cancer cells. We found that Dounce homogenization by hand, rather than the typical sonication or syringe lysis method, recovered surface/membrane proteins more consistently and effectively. This was indicated by marker membrane proteins such as claudin-4 and EGFR (epidermal growth factor receptor) that span the typical 20-200 kD range. As monitored by Western blotting (WB), the Dounce lysis method combined with cell surface biotinylation showed consistent recovery of the marker proteins claudin-4 and EGFR. This lysis method was combined with a cell surface biotinylation strategy to enrich cell surface/membrane proteins using affinity bead-based purification with four-fold less cells compared to prior work. Subsequent LC/MS/MS analysis identified 49 additional surface/membrane proteins for the first time from HCT 116 cells. This combination of methodologies may fit into an advanced workflow for identifying new and elusive cell surface proteins. It can increase the protein coverage for biomarker discovery for colorectal cancer or other cancers. This new detection/analysis approach may also promote new applications in surface display systems as well as cell screening, selection, and binding processes.

PD-L1 detection using 89Zr-atezolizumab immuno-PET in renal cell carcinoma tumorgrafts from a patient with favorable nivolumab response

BackgroundProgrammed death-ligand 1 (PD-L1) expression in metastatic renal cell carcinoma (RCC) correlates with a worse prognosis, but whether it also predicts responsiveness to anti-PD-1/PD-L1 therapy remains unclear. Most studies of PD-L1 are limited by evaluation in primary rather than metastatic sites, and in biopsy samples, which may not be representative. These limitations may be overcome with immuno–positron emission tomography (iPET), an emerging tool allowing the detection of cell surface proteins with radiolabeled antibodies. Here, we report iPET studies of PD-L1 in a preclinical tumorgraft model of clear cell RCC (ccRCC) from a patient who had a favorable response to anti-PD-1 therapy.Case presentationA 49-year-old man underwent a cytoreductive nephrectomy in 2017 of a right kidney tumor invading into the adrenal gland that was metastatic to the lungs and a rib. Histological analyses revealed a ccRCC of ISUP grade 4 with extensive sarcomatoid features. IMDC risk group was poor. Within two hours of surgery, a tumor sample was implanted orthotopically into NOD/SCID mice. Consistent with an aggressive tumor, a renal mass was detected 18 days post-implantation. Histologically, the tumorgraft showed sarcomatoid differentiation and high levels of PD-L1, similar to the patient’s tumor. PD-L1 was evaluated in subsequently transplanted mice using iPET and the results were compared to control mice implanted with a PD-L1-negative tumor. We labeled atezolizumab, an anti-PD-L1 antibody with a mutant Fc, with zirconium-89. iPET revealed significantly higher 89Zr-atezolizumab uptake in index than control tumorgrafts. The patient was treated with high-dose IL2 initially, and subsequently with pazopanib, with rapidly progressive disease, but had a durable response with nivolumab.ConclusionsTo our knowledge, this is the first report of non-invasive detection of PD-L1 in renal cancer using molecular imaging. This study supports clinical evaluation of iPET to identify RCC patients with tumors deploying the PD-L1 checkpoint pathway who may be most likely to benefit from PD-1/PD-L1 disrupting drugs.

Chip-based sensing for release of unprocessed cell surface proteins in vitro and in serum and its (patho)physiological relevance.

To study the possibility that certain components of eukaryotic plasma membranes are released under certain (patho)physiological conditions, a chip-based sensor was developed for the detection of cell surface proteins, which are anchored at the outer leaflet of eukaryotic plasma membranes by a covalently attached glycolipid, exclusively, and might be prone to spontaneous or regulated release on the basis of their amphiphilic character. For this, unprocessed, full-length glycosylphosphatidylinositol-anchored proteins (GPI-AP), together with associated phospholipids, were specifically captured and detected by a chip- and microfluidic channel-based sensor, leading to changes in phase and amplitude of surface acoustic waves (SAW) propagating over the chip surface. Unprocessed GPI-AP in complex with lipids were found to be released from rat adipocyte plasma membranes immobilized on the chip, which was dependent on the flow rate and composition of the buffer stream. The complexes were identified in the incubation medium of primary rat adipocytes, in correlation to the cell size, and in rat as well as human serum. With rats, the measured changes in SAW phase shift, reflecting specific mass/size or amount of the unprocessed GPI-AP in complex with lipids, and SAW amplitude, reflecting their viscoelasticity, enabled the differentiation between the lean and obese (high-fat diet) state, and the normal (Wistar) and hyperinsulinemic (Zucker fatty) as well as hyperinsulinemic hyperglycemic (Zucker diabetic fatty) state. Thus chip-based sensing for complexes of unprocessed GPI-AP and lipids reveals the inherently labile anchorage of GPI-AP at plasma membranes and their susceptibility for release in response to (intrinsic/extrinsic) cues of metabolic relevance and may, therefore, be useful for monitoring of (pre-)diabetic disease states.

Proximity Hybridization-Regulated Immunoassay for Cell Surface Protein and Protein-Overexpressing Cancer Cells via Electrochemiluminescence.

A simple electrochemiluminescence (ECL) immunoassay based on a proximity hybridization-regulated strategy was developed for highly sensitive and specific detection of cell surface protein and protein-overexpressing cancer cells. A biosensor was fabricated by self-assembling a thiolated capture ss-DNA3 (partially hybridize with ss-DNA1 and ss-DNA2) and blocking with 6-mercapto-1-hexanol on a gold electrode surface. Target protein was simultaneously bound by two ss-DNA-tagged antibody probes (DNA1-Ab1 and DNA2-Ab2), while DNA1 and DNA2 were brought in sufficient proximity and hybridized with capture DNA3 on the surface of the biosensor. After ECL signal reagent Ru(phen)32+ was intercalated into the hybridized ds-DNAs, ECL measurement was performed in the coreactant solution. A "signal on" proximity hybridization-regulated ECL immunoassay for alpha-fetoprotein (AFP) was developed. The ECL intensity increased with the increase of AFP concentration in the range of 0.05-20.0 ng/mL with a detection limit of 6.2 pg/mL. Moreover, the developed ECL method was successfully used to detect AFP-overexpressing cancer cells (MCF-7 cancer cells as model) with a detection limit of 620 cells/mL (∼60 MCF-7 cells in 100 μL of cell suspension) and discriminate AFP expression on different types of the living cell surface. This work for the first time reports a proximity hybridization-regulated ECL immunoassay for the detection of the cell surface protein on a living cell surface with good specificity and sensitivity. This simple, specific, and sensitive strategy is greatly promising for the detection of proteins and specific cells.

Binding-responsive catalysis of Taq DNA polymerase for the sensitive and selective detection of cell-surface proteins.

Here we develop a new method for the sensitive and selective detection of cell-surface proteins with an aptamer probe designed for binding-responsive catalysis of Taq DNA polymerase. Taking the biotin receptor as a model, the method allows the detection of target protein on surfaces of different types of cancer cells.

Cell Surface Protein Detection to Assess Receptor Internalization.

The migration of membrane receptors upon exposure to different stimulants/inhibitors is of great importance. Among others, the internalization of membrane receptors affects their accessibility to ligands and cell responsiveness to environmental cues. Experimentally, receptor internalization can be used as a measure of their activation. In our studies, we employed this approach to explore cross-talk between a seven transmembrane domain receptor for neuropeptide Y (NPY), Y5R, and a tyrosine kinase receptor for brain-derived neurotrophic factor (BDNF), TrkB. To this end, we measured the internalization of Y5R upon stimulation with the TrkB ligand, BDNF. Upon treatment with BDNF, the cells were exposed to a membrane impermeable, biotinylation reagent that selectively labels surface proteins. Subsequently, the biotinylated membrane proteins were affinity-purified on columns with avidin resins and analyzed by Western blot. Differences in the fraction of receptors present on the cell surface of control and ligand-treated cells served as a measure of their internalization and response to particular stimuli.

Circulating tumor cells in sarcomas: a brief review.

Although rare, sarcomas represent a source of significant morbidity and mortality with nearly one reported death for every two new diagnoses. The detection and surveillance of circulating tumor cells (or CTCs) has been found to have significant clinical utility in epithelial malignancies, such as carcinoma of the colon, breast and prostate. Here, we summarize what is known regarding CTCs in sarcomas. Although still in its relative infancy, the detection of CTCs in sarcoma patients may help to diagnose and predict recurrence or metastasis as well as improve the overall management of sarcoma patients. CTCs are most often detected via reverse transcriptase polymerase chain reaction or antibody-based detection of cell surface proteins, including flow cytometry. Samples may be obtained from either peripheral blood or bone marrow. CTC detection in translocation sarcomas is perhaps most promising, as a recurrent abnormal gene fusion product can be detected in involved individuals but not in the normal patient. Studies in Ewing's sarcoma/peripheral neuroectodermal tumor, synovial sarcoma and alveolar soft part sarcoma have confirmed the feasibility of this approach. Other investigators have turned toward detection of more universal markers of sarcomas, such as the pan-mesenchymal marker Vimentin. In the case of osteosarcoma, more specific markers of osteogenic differentiation (Type I Collagen) have been utilized. In summary, although in its relative nascency, the use of CTC detection for the management of sarcoma patients shows initial promise.

Fluorogen-Activating scFv Biosensors Target Surface Markers on Live Cells Via Streptavidin or Single-Chain Avidin

Fluorescence biosensors are indispensable tools for understanding protein behavior and function in cells. Recent advancements utilize fluorogen-activating-proteins (FAPs) that form complexes with small organic molecules (fluorogens) and result in their fluorescence activation. The technology has found multiple uses in protein discovery applications; however, the current method of detection requires the expression of FAPs as gene fusion tags in cells-a process that is time- and labor-intensive. In this report, we present an alternate method that utilizes FAPs as affinity reagents. Accordingly, we isolated soluble reagents based on FAP fusions with streptavidin (Strep) or avidin proteins, both highly selective for biotin. When tested in vitro, the reagents displayed bi-functional activity, fluorogen activation, and biotin affinity. For live-cell protein discovery, surface targets were biotinylated via biotin-tagged immunoglobulins or a genetically encoded biotin acceptor peptide. As a result, when the cells were labeled with FAP-Strep or FAP-avidin reagent, the in vivo fluorescence measurements indicated high target specificity, minimal background, and bright signal detection. In summary, we present a novel FAP reagent platform that offers a rapid and efficient approach for cell surface protein detection.

Proteomic Analysis Reveals Drug Accessible Cell Surface N-Glycoproteins of Primary and Established Glioblastoma Cell Lines

Glioblastoma is the most common primary brain tumor in adults with low average survival time after diagnosis. In order to improve glioblastoma treatment, new drug-accessible targets need to be identified. Cell surface glycoproteins are prime drug targets due to their accessibility at the surface of cancer cells. To overcome the limited availability of suitable antibodies for cell surface protein detection, we performed a comprehensive mass spectrometric investigation of the glioblastoma surfaceome. Our combined cell surface capturing analysis of primary ex vivo glioblastoma cell lines in combination with established glioblastoma cell lines revealed 633 N-glycoproteins, which vastly extends the known data of surfaceome drug targets at subcellular resolution. We provide direct evidence of common glioblastoma cell surface glycoproteins and an approximate estimate of their abundances, information that could not be derived from genomic and/or transcriptomic glioblastoma studies. Apart from our pharmaceutically valuable repertoire of already and potentially drug-accessible cell surface glycoproteins, we built a mass-spectrometry-based toolbox enabling directed, sensitive, and repetitive glycoprotein measurements for clinical follow-up studies. The included Skyline Glioblastoma SRM assay library provides an elevated starting point for parallel testing of the abundance level of the detected glioblastoma surfaceome members in future drug perturbation experiments.

Improved detection of cell surface proteins using an electrochemiluminescent cell-binding assay

Cell surface protein profiling is a generic tool to determine the quality of cultured mammalian cell lines. Flow cytometry is commonly employed as the screening technique of choice, but it consumes a large quantity of cells. We have evaluated an electrochemiluminescent (ECL)-based platform, the Meso Scale Discovery® (MSD®) Sector 6000 Imager, for cell surface protein detection with fewer than 100 cells per well. The detection of CD13 on human foreskin fibroblast (HFF) cells was evaluated using indirect detection of the reverse-phase immunoassays in 96-well and 384-well plate formats. The study has shown robust cell surface detection of CD13 on HFF cells using the 384-well plate format, with a LOD of 15.3±6.5 cells (n=3). The 96-well plate format exhibited far greater variability between experiments, such that the best LOD obtained was 42.5 cells per well. We have demonstrated, with our model system, the feasibility to perform cell-binding assays with as few as 15 cells per well of a 384-well microplate using the MSD® platform.

Cell surface protein detection with immunogold labelling in ESEM: Optimisation of the method and semi‐quantitative analysis

In this work we used a combination of immunogold labelling (IGL) and environmental scanning electron microscopy (ESEM) to detect the presence of a protein on the cell surface. To achieve this purpose we chose as experimental system 3T3 Swiss Albino Mouse Fibroblasts and galectin-3. This protein, whose sub-cellular distribution is still under discussion, is involved in a large number of cell physiological and pathological processes. IGL technique has been utilised by many authors in combination with SEM and TEM to obtain the identification/localisation of receptors and antigens, both in cells and tissues. ESEM represents an important tool in biomedical research, since it does not require any severe processing of the sample, lowering the risk of generating artefacts and interfere with IGL procedure. The absence of metal coating could yield further advantages for our purpose as the labelling detection is based on the atomic number difference between Nanogold spheres and the biological material. Using the gaseous secondary electron detector (GSED) compositional contrast is easily revealed by the backscattered electrons component of the signal. In spite of this fact, only few published papers present a combination of ESEM and IGL. Hereby we present our method, optimised to improve the intensity and the specificity of the labelling signal, in order to obtain a semi-quantitative evaluation of the labelling signal.

The development of a ‘labeless’ immunosensor for the detection of Listeria monocytogenes cell surface protein, Internalin B

Electrochemical impedance spectroscopy (EIS) is a widely used technique for probing bioaffinity interactions at the surfaces of electrically conducting polymers. EIS methods can be employed to investigate ‘labeless’ detection of analytes via impedimetric transduction. This paper describes the development of a direct immunosensor for the detection of a cell-surface protein on Listeria monocytogenes, an extremely important food-borne pathogen. L. monocytogenes are facultative anaerobic, non-sporing, Gram-positive, motile rods that employ the surface bound protein, Internalin B (InlB), to promote invasion into host cells. A recombinant form of InlB was previously cloned and expressed in Escherichia coli and a panel of antibodies and antibody fragments directed against the protein were also produced. Here, we describe how a portion of the recombinant InlB protein, the F3 fragment, and an anti-InlB polyclonal antibody, were used to develop a platform for the labeless immunosensing of InlB. Sensors were fabricated by electropolymerisation of planar screen-printed carbon electrodes with polyaniline (PANI), to produce a conductive substrate. Polyclonal anti-InlB antibody was subsequently incorporated onto the PANI layer using a biotin–avidin system for site-specific immobilisation. The sensors were then probed with varying concentrations of InlB antigen and the impedimetric response at each concentration was recorded. An anti-IgG antibody was immobilised at the electrode surface, as a control and subsequently exposed to the same concentrations of InlB. Impedimetric data for the control sensors were also recorded. Upon exposure to a range of concentrations of antigen, complex plane impedance analyses were used to relate the differing redox states of the polymer layer, to the possible charge transfer at the surface, with respect to the related mechanisms between the antibody and the polymer. These effects were subsequently monitored to assess the impedance of the polymer thereby determining the amount of bound antigen at the sensor surface. Calibration profiles for both sample (InlB) and control (IgG) sensors were constructed. A limit of detection of 4.1 pg/ml was achieved for Internalin B.