Nanostructures and molecular force bases of a highly sensitive capacitive immunosensor

Cancer immunosensor based on apo and holo transferrin binding

An electrochemical immunosensor was developed for the determination of apo-Tf (non-iron-bound) and holo-Tf (iron-bound) using polyclonal antibody transferrin (anti-Tf) immobilized at an electrode surface as a biorecognition platform. The monitoring was based on the anti-Tf binding with both Tf forms which allows the detection of cancer cells due to the constant iron cycle and the overexpression of anti-Tf on the cancer cell surface. The immunosensor characterization was performed using electrochemical impedance spectroscopy (EIS), which evaluated the impedimetric biorecognition of the antigens-antibody by the use of K₄Fe(CN)₆ redox group. The immunosensor was able to detect both forms of Tf in terms of charge transfer resistance (R_ct). Analytical curves showed a limit of detection of 0.049 and 0.053 ng mL^-1 for apo-Tf and holo-Tf, respectively. The immunosensor was applied to the detection of the two cancer cells A549 (lung carcinoma) and MCF-7 (breast carcinoma) and compared with BHK570, a healthy cell line. The impedimetric response of healthy cells differs significantly from that of the cancerous cells, as revealed by a Dunnett's test in 95% confidence level-ca. 10² cells mL^-1-indicating the feasibility of the immunosensor to discriminate both types of cells. The indirect detection of anti-Tf based on apo-Tf and holo-Tf binding can be considered an advanced approach for cancer recognition. Graphical abstract.

An atomic-force basis for the bacteriolytic effects of granulysin

While granulysin has been suggested to play an important role in adaptive immune responses against bacterial infections by killing pathogens, and molecular force for protein-protein interaction or protein-bacteria interaction may designate the specific functions of a protein, the molecular-force basis underlying the bacteriolytic effects of granulysin at single-molecule level remains unknown. Here, we produced and purified bactericidal domain of macaque granulysin (GNL). Our bacterial lysis assays suggested that GNL could efficiently kill bacteria such as Listeria monocytogenes. Furthermore, we found that the interaction force between GNL and L. monocytogenes measured by an atomic force microscopy (AFM) was about 22.5 pN. Importantly, our AFM-based single molecular analysis suggested that granulysin might lyse the bacteria not only through electrostatic interactions but also by hydrogen bonding and van der Waals interaction. Thus, this work provides a previous unknown mechanism for bacteriolytic effects of granulysin.

NSOM/QD-based direct visualization of CD3-induced and CD28-enhanced nanospatial coclustering of TCR and coreceptor in nanodomains in T cell activation

Direct molecular imaging of nano-spatial relationship between T cell receptor (TCR)/CD3 and CD4 or CD8 co-receptor before and after activation of a primary T cell has not been reported. We have recently innovated application of near-field scanning optical microscopy (NSOM) and immune-labeling quantum dots (QD) to image Ag-specific TCR response during in vivo clonal expansion, and now up-graded the NSOM/QD-based nanotechnology through dipole-polarization and dual-color imaging. Using this imaging system scanning cell-membrane molecules at a best-optical lateral resolution, we demonstrated that CD3, CD4 or CD8 molecules were distinctly distributed as single QD-bound molecules or nano-clusters equivalent to 2–4 QD fluorescence-intensity/size on cell-membrane of un-stimulated primary T cells, and ∼6–10% of CD3 were co-clustering with CD4 or CD8 as 70–110 nm nano-clusters without forming nano-domains. The ligation of TCR/CD3 on CD4 or CD8 T cells led to CD3 nanoscale co-clustering or interaction with CD4 or CD8 co-receptors forming 200–500 nm nano-domains or >500 nm micro-domains. Such nano-spatial co-clustering of CD3 and CD4 or CD3 and CD8 appeared to be an intrinsic event of TCR/CD3 ligation, not purely limited to MHC engagement, and be driven by Lck phosphorylation. Importantly, CD28 co-stimulation remarkably enhanced TCR/CD3 nanoscale co-clustering or interaction with CD4 co-receptor within nano- or micro-domains on the membrane. In contrast, CD28 co-stimulation did not enhance CD8 clustering or CD3–CD8 co-clustering in nano-domains although it increased molecular number and density of CD3 clustering in the enlarged nano-domains. These nanoscale findings provide new insights into TCR/CD3 interaction with CD4 or CD8 co-receptor in T-cell activation.

NSOM- and AFM-based nanotechnology elucidates nano-structural and atomic-force features of a Y. pestis V immunogen-containing particle vaccine capable of eliciting robust response

It is postulated that unique nanoscale proteomic features of immunogen on vaccine particles may determine immunogen-packing density, stability, specificity, and pH-sensitivity on the vaccine particle surface and thus impact the vaccine-elicited immune responses. To test this presumption, we employed near-filed scanning optical microscopy (NSOM)- and atomic force microscopy (AFM)-based nanotechnology to study nano-structural and single-molecule force bases of Yersinia pestis (Y. pestis) V immunogen fused with protein anchor (V-PA) loaded on gram positive enhancer matrix (GEM) vaccine particles. Surprisingly, the single-molecule sensitive NSOM revealed that approximately 90% of V-PA immunogen molecules were packed as high-density nanoclusters on GEM particle. AFM-based single-molecule force analyses indicated a highly stable and specific binding between V-PA and GEM at the physiological pH. In contrast, this specific binding was mostly abrogated at the acidic pH equivalent to the biochemical pH in phagolysosomes of antigen-presenting-cells in which immunogen protein is processed for antigen presentation. Intranasal mucosal vaccination of mice with such immunogen loaded on vaccine particles elicited robust antigen-specific immune response. This study indicated that high-density, high-stability, specific, and immunological pH-responsive loading of immunogen nanoclusters on vaccine particles could readily be presented to the immune system for induction of strong antigen-specific immune responses.

NSOM/QD-based nanoscale immunofluorescence imaging of antigen-specific T-cell receptor responses during an in vivo clonal Vγ2Vδ2 T-cell expansion

Nanoscale imaging of an in vivo antigen-specific T-cell immune response has not been reported. Here, the combined near-field scanning optical microscopy- and fluorescent quantum dot-based nanotechnology was used to perform immunofluorescence imaging of antigen-specific T-cell receptor (TCR) response in an in vivo model of clonal T-cell expansion. The near-field scanning optical microscopy/quantum dot system provided a best-optical-resolution (<50 nm) nano-scale imaging of Vgamma2Vdelta2 TCR on the membrane of nonstimulated Vgamma2Vdelta2 T cells. Before Ag-induced clonal expansion, these nonstimulating Vgamma2Vdelta2 TCRs appeared to be distributed differently from their alphabeta TCR counterparts on the cell surface. Surprisingly, Vgamma2Vdelta2 TCR nanoclusters not only were formed but also sustained on the membrane during an in vivo clonal expansion of Vgamma2Vdelta2 T cells after phosphoantigen treatment or phosphoantigen plus mycobacterial infection. The TCR nanoclusters could array to form nanodomains or microdomains on the membrane of clonally expanded Vgamma2Vdelta2 T cells. Interestingly, expanded Vgamma2Vdelta2 T cells bearing TCR nanoclusters or nanodomains were able to rerecognize phosphoantigen and to exert better effector function. These studies provided nanoscale insight into the in vivo T-cell immune response.