Kinetic analysis of interactions between bispecific monoclonal antibodies and immobilized antigens using a resonant mirror biosensor

First-passage time analysis of diffusion-controlled reactions in single-molecule detection

Single-molecule detection (SMD) aims to achieve the ultimate limit-of-detection (LOD) in biosensing. This method detects a countable number of targeted analyte molecules in solution, where the dynamics of molecule diffusion, capturing, identification and delivery greatly impact the SMD's efficiency and accuracy. In this study, we adopt the first-passage time method to investigate the diffusion-controlled reaction process in SMD. We analyze the influence of detection conditions on incubation time and the expected coefficient of variation (CV) under three SMD molecule capturing strategies, including solid-phase capturing (one-dimensional solid-liquid interface fixation), liquid-phase magnetic bead (MB) capturing, and liquid-phase direct fluorescence pair labeling. We find that inside a finite-sized reaction chamber, a finite average reaction time exists in all three capturing strategies, while the liquid-phase strategies are in general more efficient than the solid-phase approaches. CV can be estimated by averaging first-passage time solely in all three strategies, and the CV reduction is achievable given an extended reaction time. To further enable zeptomolar detection, extra treatments, such as adopting liquid-phase fluorescence pairs with high diffusion rates to label the molecule, or designing specific sensing devices with large effective sensing areas would be required. This framework provides solid theoretical support to guide the design of SMD sensing strategies and sensor structures to achieve desired measurement time and CV.

Trend of telomerase activity change during human iPSC self-renewal and differentiation revealed by a quartz crystal microbalance based assay

Telomerase plays an important role in governing the life span of cells for its capacity to extend telomeres. As high activity of telomerase has been found in stem cells and cancer cells specifically, various methods have been developed for the evaluation of telomerase activity. To overcome the time-consuming procedures and complicated manipulations of existing methods, we developed a novel method named Telomeric Repeat Elongation Assay based on Quartz crystal microbalance (TREAQ) to monitor telomerase activity during the self-renewal and differentiation of human induced pluripotent stem cells (hiPSCs). TREAQ results indicated hiPSCs possess invariable telomerase activity for 11 passages on Matrigel and a steady decline of telomerase activity when differentiated for different periods, which is confirmed with existing golden standard method. The pluripotency of hiPSCs during differentiation could be estimated through monitoring telomerase activity and compared with the expression levels of markers of pluripotency gene via quantitative real time PCR. Regular assessment for factors associated with pluripotency or stemness was expensive and requires excessive sample consuming, thus TREAQ could be a promising alternative technology for routine monitoring of telomerase activity and estimate the pluripotency of stem cells.

Theory and applications of surface plasmon resonance, resonant mirror, resonant waveguide grating, and dual polarization interferometry biosensors

Biosensors have been used extensively in the scientific community for several purposes, most notably to determine association and dissociation kinetics, protein-ligand, protein-protein, or nucleic acid hybridization interactions. A number of different types of biosensors are available in the field, each with real or perceived benefits over the others. This review discusses the basic theory and operational arrangements of four commercially available types of optical biosensors: surface plasmon resonance, resonant mirror, resonance waveguide grating, and dual polarization interferometry. The different applications these techniques offer are discussed from experiments and results reported in recently published literature. Additionally, recent advancements or modifications to the current techniques are also discussed.

Label-free detection with the resonant mirror biosensor

The resonant mirror (RM) biosensor is a leaky waveguide-based instrument that uses the evanescent field to probe changes in the refractive index at the sensing surface.The RM can therefore be used to monitor in real-time and label-free the interaction between an analyte in solution and its biospecific partner immobilized on the waveguide surface.The RM has been used in studying the interaction of a variety of moieties including proteins, carbohydrates, cells, nucleic acids and receptors, leading to applications in areas such as clinical diagnostics, homeland security, and pharmaceutical and biomolecular interactions. This chapter will review the principle of this biosensor, and the recent advances in instrumentation, different immobilization chemistries, and kinetic studies, as well as some applications.

Comparison of a Resonant Mirror Biosensor (IAsys) and a Quartz Crystal Microbalance (QCM) for the Study on Interaction between Paeoniae Radix 801 and Endothelin-1

A resonant mirror biosensor, IAsys, and a quartz crystal microbalance (QCM) are known independently as surface sensitive analytical devices capable of label-free and in situ bioassays. In this study, an IAsys and a QCM are employed for a new study on the action mechanism of Paeoniae Radix 801 (P. radix 801) by detecting the specific interaction between P. radix 801 and endothelin-1 (ET-1). In the experiments, ET-1 was immobilized on the surfaces of the IAsys cuvette and the QCM substrate by surface modification techniques, and then P. radix 801 solution was contacted to the cuvette and the substrate, separately. Then, the binding and interaction process between P. radix 801 and ET-1 was monitored by IAsys and QCM, respectively. The experimental results showed that P. radix 801 binds ET-1 specifically. The IAsys and QCM response curves to the ET-1 immobilization and P. radix 801 binding are similar in reaction process, but different in binding profiles, reflecting different resonation principles. Although both IAsys and QCM could detect the interaction of P. radix 801 and ET-1 with high reproducibility and reliability through optimization of the ET-1 coating, the reproducibility and reliability obtained by IAsys are better than those obtained by QCM, since the QCM frequency is more sensitive to temperature fluctuations, atmospheric changes and mechanical disturbances. However, IAsys and QCM are generally potent and reliable tools to study the interaction of P. radix 801 and ET-1, and can conclusively be applied to the action mechanism of P. radix 801.

Quantitative and label-free technique for measuring protease activity and inhibition using a microfluidic cantilever array

We report the use of a SiN x based gold coated microcantilever array to quantitatively measure the activity and inhibition of a model protease immobilized on its surface. Trypsin was covalently bound to the gold surface of the microcantilever using a synthetic spacer, and the remaining exposed silicon nitride surface was passivated with silanated polyethylene glycol. The nanoscale cantilever motions induced by trypsin during substrate turnover were quantitatively measured using an optical laser-deflection technique. These microcantilever deflections directly correlated with the degree of protease turnover of excess synthetic fibronectin substrate ( K M = 0.58 x 10 (-6) M). Inhibition of surface-immobilized trypsin by soybean trypsin inhibitor (SBTI) was also observed using this system.

Electrophoresis mobility shift assay and biosensor used in studying the interaction between bleomycin A5 and DNA

DNA is the potential target of numerous drugs utilized widely in clinical cancer therapy. Here we employed bleomycin A5, with its deactivated form as contrast, to investigate the interaction between small pharmaceutical and DNA. Electrophoresis mobility shift assay (EMSA) which is a common technique used in studying specific interactions between DNA and proteins is applied in visualizing the binding of bleomycin A5 with DNA intuitively. More accurate association equilibrium constant for native and deactivated bleomycin A5 to DNA achieved on biosensor IAsys AUTO+ is 1.25x10(4) and 1.3x10(3) M(-1), respectively. With combination of EMSA and biosensor, a qualitative and quantitative method is described, which can be extended to studying the binding of most small molecules with targeting DNA and serves as a powerful tool in designing and screening for novel drugs.

Tentacle probes: eliminating false positives without sacrificing sensitivity

The majority of efforts to increase specificity or sensitivity in biosensors result in trade-offs with little to no gain in overall accuracy. This is because a biosensor cannot be more accurate than the affinity interaction it is based on. Accordingly, we have developed a new class of reagents based on mathematical principles of cooperativity to enhance the accuracy of the affinity interaction. Tentacle probes (TPs) have a hairpin structure similar to molecular beacons (MBs) for enhanced specificity, but are modified by the addition of a capture probe for increased kinetics and affinity. They produce kinetic rate constants up to 200-fold faster than MB with corresponding stem strengths. Concentration-independent specificity was observed with no false positives at up to 1 mM concentrations of variant analyte. In contrast, MBs were concentration dependent and experienced false positives above 3.88 μM of variant analyte. The fast kinetics of this label-free reagent may prove important for extraction efficiency, hence sensitivity and detection time, in microfluidic assays. The concentration-independent specificity of TPs may prove extremely useful in assays where starting concentrations and purities are unknown as would be the case in bioterror or clinical point of care diagnostics.

Development and evaluation of realistic microbioassays in freely suspended droplets on a chip

A novel technique for biomolecular detection in microliter droplets floating on the surface of high density oil is presented. Each droplet was captured and manipulated dielectrophoretically and was used as a site for a microscopic bioassay based on agglutination of antibody-conjugated particles. The results were read out by the pattern of unagglomerated gold nanoparticles collected on the droplet surface. Two formats of bioassays, namely gold only agglutination and gold and latex agglutination, were investigated experimentally by varying analyte concentration, particle size and concentration, number of antigen binding sites per particle, time for incubation, and rate of particle collection on the droplet surface. The microbioassays performance was also evaluated with ricin antibodies and compared to the ricin assays in field use. It is estimated that the droplet based assays require 100x smaller sample volume and are ten times more sensitive, though they require longer times to complete. The experiments were interpreted by modeling the kinetics of particle agglutination and mass transfer processes inside the droplets. The incubation time and antigen concentration values calculated by the model correlate well with the experimental results. The results could allow for development of efficient immunoassays on a chip requiring even smaller sample volumes.

Adhesion characteristics of Listeria adhesion protein (LAP)-expressing Escherichia coli to Caco-2 cells and of recombinant LAP to eukaryotic receptor Hsp60 as examined in a surface plasmon resonance sensor

Listeria adhesion protein (LAP) is an important adhesion factor in Listeria monocytogenes and interacts with its cognate receptor, mammalian heat shock protein 60 (Hsp60). The genetic identity of LAP was determined to be alcohol acetaldehyde dehydrogenase (Aad). A recombinant Escherichia coli strain expressing aad confirmed the involvement of Aad in adhesion to Caco-2 cells. Binding kinetics (ka) of recombinant LAP (rLAP) to Hsp60 was examined in a surface plasmon resonance sensor and was determined to be 5.35 x 10(8) M(-1) s(-1) and it was equivalent to the binding of anti-Hsp60 antibody (ka = 2.15 x 10(9) M(-1) s(-1)) to Hsp60. In contrast, Internalin B, an adhesion/invasion protein from L. monocytogenes, used as a control, had binding kinetics (ka) of only 2.9 x 10(6) M(-1) s(-1). The KD value of rLAP was 1.68 x 10(-8) M, which was significantly lower than Internalin B (KD = 6.5 x 10(-4) M). These results suggest that Hsp60 has significantly higher avidity for anti-Hsp60 antibody and LAP than Internalin B. In summary, LAP is identified as an alcohol acetaldehyde dehydrogenase and binding of recombinant E. coli to Caco-2 cells or rLAP to Hsp60 protein was found to be highly specific.

Effects of propyl gallate on interaction between TNF-alpha and sTNFR-I using an affinity biosensor

AIM

To study the effects of propyl gallate on the interaction of tumor necrosis factor-alpha (TNF-alpha) with its soluble receptor, sTNFR-I.

METHODS

Interactions between TNF-alpha and sTNFR-I were analyzed using an IAsys biosensor. sTNFR-I was immobilized on the carboxymethyl dextran (CMD) surface of the IAsys biosensor cuvettes, and TNF-alpha preincubated with different concentrations of propyl gallate was added to the cuvettes. The resonant angle shift caused by the binding between TNF-alpha and sTNFR-I was then recorded.

RESULTS

sTNFR-I was immobilized on the CMD surface at a density of 2.76 ng/mm(2). TNF-alpha then bound the immobilized sTNFR-I specifically, and propyl gallate was able to enhance the binding between TNF-alpha and sTNFR-I in a dose-dependent manner.

CONCLUSION

The binding between TNF-alpha and sTNFR-I is one of the targets that propyl gallate can act on in vivo. The IAsys biosensor offers a new clue as to the study on the mechanisms of action of propyl gallate.

Interaction of daunomycin antibiotic with human serum albumin: Investigation by resonant mirror biosensor technique, fluorescence spectroscopy and molecular modeling methods

Daunomycin (DM) is a clinically used antitumor anthracycline antibiotic, which is transported primarily by human serum albumin (HSA) in the blood. Binding characteristics are therefore of interest for both the pharmacokinetics and pharmacodynamics of DM. A new optical biosensor technique based on the resonant mirror was used to characterize interaction of DM with HSA at different temperatures and the affinity constants were obtained. The HSA-DM interaction is exothermic with having favorable enthalpy and entropy followed by the integrated van't Hoff equation analysis. Fluorescence studies showed that DM has an ability to quench the intrinsic fluorescence of HSA through a static quenching procedure according to the Stern-Volmer equation and DM displays a pH-dependent binding affinity to HSA. Molecular modeling calculations showed that the DM binds HSA to a non-classical drug binding site and further analysis of the binding site of DM within the HSA molecule suggested that hydrophobic contacts, hydrogen bond formation and electrostatic interactions account for the binding of DM.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.