BSI technology Literature

Journal references, abstracts,  presentations, and company collateral are excellent resources for exploring the many ways in which BSI technology is being put to work in life science and medical research. We encourage you to return often to this page to keep abreast of new developments in Back-Scattering Interferometry.


BROCHURE: Back-Scattering Interferometry with Conformation-Sensitive Detection
A NEW ERA IN DRUG DISCOVERY: Back-Scattering Interferometry (BSI) provides direct binding Kd determinations with label-free, conformation-sensitive detection, delivering significant advantages versus conventional methods for intractable drug targets in complex matrices.


SPEC SHEET: TruBind BSI System 100
The TruBind™ BSI System 100 is proven to deliver vital data, informing drug discovery efforts from secondary screening through to IND submission.


APP NOTE: Label-free, Free-Solution Binding Characterization of Bcr-Abl Kinase Inhibitors by BSI
Because BSI evaluates direct target engagement independent of downstream activity, BSI is aptly suited to advance efforts in the discovery of new type II and allostery driven type III inhibitors to Bcr-Abl Kinase as well as other valuable kinase targets of medical import.


WHITE PAPER: The Role of BSI in the Discovery and Development of Allosteric Ligands
By enabling direct quantitative binding measurements of compounds to receptors in a native-like membrane matrix without the use of labels, surface tethering, or other complex assay set-up procedures, BSI is poised to greatly accelerate the pace of allosteric drug discovery.


TRUBIND AT WORK: Measuring Protein-Protein Interactions (PPI)
BSI isn’t limited by label, tethering or size restrictions, thereby enabling true binding and inhibition to be directly monitored.


TRUBIND AT WORK: Measuring Kinase Small Molecule Interactions
The demonstrated strengths of BSI to measure small molecule inhibitor binding to both active and nonactivated Bcr-Abl combined with its ability to measure direct binding in allosteric systems make BSI an ideal tool for the discovery of Types II and III kinase inhibitors.


TRUBIND AT WORK: Targeting GPCRs with Small Molecule Allosterics
TruBind BSI Technology delivers key benefits in the investigation of GPCR inhibitors, with no tags, no surface attachments for true binding characterization.



Baclofen and other GABAB receptor Agents are Allosteric Modulators of the CXCL12 Chemokine Receptor CXDR4
GuyonA, et al., The Official Journal of the Society for Neuroscience 33(28):11643-11645 (2013)

Guyon A, Kussrow A, Olmsted IR, Sandoz G, Bornhop DJ, Nahon JL.
Université de Nice Sophia Antipolis, Nice, France. [email protected]


CXCR4, a receptor for the chemokine CXCL12 (stromal-cell derived factor-1α), is a G-protein-coupled receptor (GPCR), expressed in the immune and CNS and integrally involved in various neurological disorders. The GABAB receptor is also a GPCR that mediates metabotropic action of the inhibitory neurotransmitter GABA and is located on neurons and immune cells as well. Using diverse approaches, we report novel interaction between GABAB receptor agents and CXCR4 and demonstrate allosteric binding of these agents to CXCR4. First, both GABAB antagonists and agonists block CXCL12-elicited chemotaxis in human breast cancer cells. Second, a GABAB antagonist blocks the potentiation by CXCL12 of high-threshold Ca(2+) channels in rat neurons. Third, electrophysiology in Xenopus oocytes and human embryonic kidney cell line 293 cells in which we coexpressed rat CXCR4 and the G-protein inward rectifier K(+) (GIRK) channel showed that GABAB antagonist and agonist modified CXCL12-evoked activation of GIRK channels. To investigate whether GABAB ligands bind to CXCR4, we expressed this receptor in heterologous systems lacking GABAB receptors and performed competition binding experiments. Our fluorescent resonance energy transfer experiments suggest that GABAB ligands do not bind CXCR4 at the CXCL12 binding pocket suggesting allosteric modulation, in accordance with our electrophysiology experiments. Finally, using backscattering interferometry and lipoparticles containing only the CXCR4 receptor, we quantified the binding affinity for the GABAB ligands, confirming a direct interaction with the CXCR4 receptor. The effect of GABAergic agents on CXCR4 suggests new therapeutic potentials for neurological and immune diseases.


The Effect of Hybridization-Induced Secondary Structure Alterations on RNA using Back-Scattering Interferometry
AdamsNM, et al., Nucleic Acid Research 41 (9); e103 (2013)

Adams NM, Olmsted IR, Haselton FR, Bornhop DJ, Wright DW.
Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA.


Backscattering interferometry (BSI) has been used to successfully monitor molecular interactions without labeling and with high sensitivity. These properties suggest that this approach might be useful for detecting biomarkers of infection. In this report, we identify interactions and characteristics of nucleic acid probes that maximize BSI signal upon binding the respiratory syncytial virus nucleocapsid gene RNA biomarker. The number of base pairs formed upon the addition of oligonucleotide probes to a solution containing the viral RNA target correlated with the BSI signal magnitude. Using RNA folding software mfold, we found that the predicted number of unpaired nucleotides in the targeted regions of the RNA sequence generally correlated with BSI sensitivity. We also demonstrated that locked nucleic acid (LNA) probes improved sensitivity approximately 4-fold compared to DNA probes of the same sequence. We attribute this enhancement in BSI performance to the increased A-form character of the LNA:RNA hybrid. A limit of detection of 624 pM, corresponding to ∼10(5) target molecules, was achieved using nine distinct ∼23-mer DNA probes complementary to regions distributed along the RNA target. Our results indicate that BSI has promise as an effective tool for sensitive RNA detection and provides a road map for further improving detection limits.


BSI: an Ultrasensitive Method for the Unperturbed Detection of Acetycholinesterase-Inhibitor interactions
HaddadGL, et al., Angewandte Chemie 51 (44): 11126-11130 (2012)

Haddad GL, Young SC, Heindel ND, Bornhop DJ, Flowers RA 2nd.
Department of Chemistry, Lehigh University, Bethlehem, PA 18015, USA.


A series of inhibitors of acetylcholinesterase (AChE) have been screened by back-scattering interferometry (BSI). Enzyme levels as low as 100 pM (22,000 molecules of AChE) can be detected. This method can be used to screen for mixed AChE inhibitors, agents that have shown high efficacy against Alzheimer’s disease, by detecting dual-binding interactions. E = enzyme, I = inhibitor, S = substrate.


Evolution and Protein Packaging of Small-Molecule RNA Aptamers.
LauJL, et al., ACS Nano 2011 Oct 25;5(10):7722-9

Lau JL, Baksh MM, Fiedler JD, Brown SD, Kussrow A, Bornhop DJ, Ordoukhanian P, Finn MG.
Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, United States.


A high-affinity RNA aptamer (K(d) = 50 nM) was efficiently identified by SELEX against a heteroaryldihydropyrimidine structure, chosen as a representative drug-like molecule with no cross reactivity with mammalian or bacterial cells. This aptamer, its weaker-binding variants, and a known aptamer against theophylline were each embedded in a longer RNA sequence that was encapsidated inside a virus-like particle by a convenient expression technique. These nucleoprotein particles were shown by backscattering interferometry to bind to the small-molecule ligands with affinities similar to those of the free (nonencapsidated) aptamers. The system therefore comprises a general approach to the production and sequestration of functional RNA molecules, characterized by a convenient label-free analytical technique.


Histone Demethylase LSD1 is a Folate-Binding Protein
LukaZ, et al., Biochemistry 2011 May 31;50(21):4750-6.

Luka Z, Moss F, Loukachevitch LV, Bornhop DJ, Wagner C.
Department of Biochemistry, Vanderbilt University Medical Center, Nashville, TN 37232, USA.


Methylation of lysine residues in histones has been known to serve a regulatory role in gene expression. Although enzymatic removal of the methyl groups was discovered as early as 1973, the enzymes responsible for their removal were isolated and their mechanism of action was described only recently. The first enzyme to show such activity was LSD1, a flavin-containing enzyme that removes the methyl groups from lysines 4 and 9 of histone 3 with the generation of formaldehyde from the methyl group. This reaction is similar to the previously described demethylation reactions conducted by the enzymes dimethylglycine dehydrogenase and sarcosine dehydrogenase, in which protein-bound tetrahydrofolate serves as an accepter of the formaldehyde that is generated. We now show that nuclear extracts of HeLa cells contain LSD1 that is associated with folate. Using the method of back-scattering interferometry, we have measured the binding of various forms of folate to both full-length LSD1 and a truncated form of LSD1 in free solution. The 6R,S form of the natural pentaglutamate form of tetrahydrofolate bound with the highest affinity (K(d) = 2.8 μM) to full-length LSD1. The fact that folate participates in the enzymatic demethylation of histones provides an opportunity for this micronutrient to play a role in the epigenetic control of gene expression.


Label-free Quantification of Membrane-Ligand Interactions Using Back-Scattering Interferometry
BakshMM et al., Nat Biotechnol. 2011 Apr;29(4):357-60.

Baksh MM, Kussrow AK, Mileni M, Finn MG, Bornhop DJ.
Department of Chemistry, The Scripps Research Institute, La Jolla, California, USA.


Although membrane proteins are ubiquitous within all living organisms and represent the majority of drug targets, a general method for direct, label-free measurement of ligand binding to native membranes has not been reported. Here we show that backscattering interferometry (BSI) can accurately quantify ligand-receptor binding affinities in a variety of membrane environments. By detecting minute changes in the refractive index of a solution, BSI allows binding interactions of proteins with their ligands to be measured at picomolar concentrations. Equilibrium binding constants in the micromolar to picomolar range were obtained for small- and large-molecule interactions in both synthetic and cell-derived membranes without the use of labels or supporting substrates. The simple and low-cost hardware, high sensitivity and label-free nature of BSI should make it readily applicable to the study of many membrane-associated proteins of biochemical and pharmacological interest.



Universal Sensing by Transduction of Antibody Binding using Back-Scattering Interferometry
KussrowA et al., Chembiochem. 2011 Feb 11;12(3):367-70.

Kussrow A, Baksh MM, Bornhop DJ, Finn MG.
Department of Chemistry and Vanderbilt Institute for Chemical Biology, Vanderbilt University


All binding events induce a change in refractive index, and antibody–antigen interactions are no exception. We describe the use of backscattering interferometry to quantify antibody binding without labels and with high sensitivity. As a broad range of antibodies are available, this method represents a general way to selectively detect a wide variety of trace molecules in simple or complex mixtures.


Free-solution Interaction Assay of Carbonic Anhydrase to its Inhibitors Using Back-Scattering Interferometry
MorcosEF et al., Electrophoresis. 2010 Nov;31(22):3691-5.

Morcos EF, Kussrow A, Enders C, Bornhop D.
Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University


Back-scattering interferometry (BSI) is a label-free, free-solution, small-volume technique used for characterizing binding interactions, which is also relevant to a growing number of biosensing applications including drug discovery. Here, we use BSI to characterize the interaction of carbonic anhydrase enzyme II with five well-known carbonic anhydrase enzyme II inhibitors (± sulpiride, sulfanilamide, benzene sulfonamide, dansylamide, and acetazolamide) in the presence of DMSO. Dissociation constants calculated for each interaction were consistent with literature values previously obtained using surface plasmon resonance and fluorescence-based competition assays. Results demonstrate the potential of BSI as a drug-screening tool which is fully compatible with DMSO and does not require immobilization or labeling, therefore allowing binding interactions to be characterized in the native state. BSI has the potential for reducing labor costs, sample consumption, and assay time while providing enhanced reliability over existing techniques.


Detection of the Photosystem I:ferredoxin Complex by Back-Scattering Interferometry
SétifP et al., J Am Chem Soc. 2010 Aug 11;132(31):10620-2.

Sétif P, Harris N, Lagoutte B, Dotson S, Weinberger SR.
iBiTec-S, URA CNRS 2096, CEA Saclay, 91191 Gif sur Yvette, France. [email protected]


The dissociation constant K(d) of the photosystem I (PSI):ferredoxin complex has been measured by backscattering interferometry (BSI) with cyanobacterial PSI (350 kDa) and ferredoxin (10.5 kDa). The BSI signal, consisting of shifts for interference fringes resulting from a change in refractive index due to complex formation, was monitored as ferredoxin concentration was titrated. K(d) values of 0.14-0.38 microM were obtained with wild-type PSI whereas no complex was detectable with a PSI mutant containing a single mutation (R39Q) in the PsaE extrinsic subunit. These results are in quantitative agreement with previous functional determinations consisting in the detection of fast electron transfer within the complex. They provide evidence that the main contribution for the high affinity binding of ferredoxin to PSI is due to a single region of PsaE comprising arginine 39. They do not support the existence of a secondary binding site that could have escaped functional detection.


Backscattering Interferometry for Low Sample Consumption Molecular Interaction Screening
KussrowA et al., Journal of the Association for Laboratory Automation, Dec;14(6):341-7 (2009).

A. Kussrow, C.S. Enders, E.F. Morcos, D.J. Bornhop
Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN


Backscattering interferometry (BSI), which uses a simple optical train comprising a He—Ne laser, a microfluidic channel, and a position sensor, has now enabled the measurement of both tethered and free-solution, label-free, molecular interactions within just nanoliters of sample. The simple macro-to-micro interface allows for a highly efficient assay work flow, which has been used to interrogate molecular binding interactions between proteins, ions and protein, and small molecules and proteins, with a high dynamic range of dissociation constants (KD) and unmatched sensitivity. With this technique, the equilibrium KD for several different binding partners was determined, typically using just picomole—micromole quantities of the binding pair at physiologically relevant concentrations.


Free-solution label-free detection of alpha-crystallin chaperone interactions by back-scattering interferometry
LathamJC et al., Anal Chem. 2009 Mar 1;81(5):1865-71.

Latham JC, Stein RA, Bornhop DJ, Mchaourab HS.
Department of Chemistry and The Vanderbilt Institute for Chemical Biology, Vanderbilt University,


We report the quantitative, label-free analysis of protein-protein interactions in free solution within picoliter volumes using backscatter interferometry (BSI). Changes in the refractive index are measured for solutions introduced on a PDMS microchip allowing determination of forward and reverse rate constants for two-mode binding. Time-dependent BSI traces are directly fit using a global analysis approach to characterize the interaction of the small heat-shock protein alpha-Crystallin with two substrates: destabilized mutants of T4 lysozyme and the in vivo target betaB1-Crystallin. The results recapitulate the selectivity of alphaB-Crystallin differentially binding T4L mutants according to their free energies of unfolding. Furthermore, we demonstrate that an alphaA-Crystallin mutant linked to hereditary cataract has activated binding to betaB1-Crystallin. Binding isotherms obtained from steady-state values of the BSI signal yielded meaningful dissociation constants and establishes BSI as a novel tool for the rapid identification of molecular partners using exceedingly small sample quantities under physiological conditions. This work demonstrates that BSI can be extended to screen libraries of disease-related mutants to quantify changes in affinity and/or kinetics of binding.


Characterizing Molecular Interaction Label-free, Back-Scattering Interferometry
KussrowA et al., Screening Trends in Drug Discovery, Volume 10, April 2009.

A. Kussrow, D.J. Bornhop, N.H. Harris, S. Dotson, S. Weinberger, W.E. Rich
Molecular Sensing, Inc.

BSI is a novel interferometric technology for measuring mass-independent molecular interactions allowing quantification of binding affinity over a large dynamicrange in KD, in a homogeneous or heterogeneous assay format, and requiring just picograms to nanograms of the protein target. Unique to BSI, small molecule inhibitors and even ions interacting with high molecular weight proteins can be studied with little a priori information about the interaction system. It is our belief that BSI shows great promise in the study of molecular interactions in drug discovery, particularly for small molecule and fragment-based


Free-Solution, Label-Free Molecular Interactions Studied by Back-scattering Interferometry
BornhopDJ et al., Science. 2007 Sep 21.

Bornhop DJ, Latham JC, Kussrow A, Markov DA, Jones RD, Sørensen HS.
Department of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University


Free-solution, label-free molecular interactions were investigated with back-scattering interferometry in a simple optical train composed of a helium-neon laser, a microfluidic channel, and a position sensor. Molecular binding interactions between proteins, ions and protein, and small molecules and protein, were determined with high dynamic range dissociation constants (Kd spanning six decades) and unmatched sensitivity (picomolar Kd’s and detection limits of 10,000s of molecules). With this technique, equilibrium dissociation constants were quantified for protein A and immunoglobulin G, interleukin-2 with its monoclonal antibody, and calmodulin with calcium ion Ca2+, a small molecule inhibitor, the protein calcineurin, and the M13 peptide. The high sensitivity of back-scattering interferometry and small volumes of microfluidics allowed the entire calmodulin assay to be performed with 200 picomoles of solute.



The Potential of Novel Label-Free Technologies for Drug Discovery Applications
Presented by Geoff Holdgate, AstraZeneca UK, during ELRIG (European Laboratory Robotics Interest Group) on September 2012 in Manchester, UK

1. Introduction to Label-free Methods
2. Drug Discovery Applications
3. Case Studies
4. Summary

The real value of label-free:
• Highly sensitive, information rich methods that have a wide application across the early drug discovery value chain
• Ability to use in combination with other label-free, biochemical or cell-based methods for improved success rates
• Increased application and understanding of the power of combinations of label-free and traditional assays will help to improve in vivo activity predictions


Free-Solution, Label-free Analysis of Membrane Protein Targets by Back-Scattering Interferometry
Presented by Scot R. Weinberger, Co-Founder and EVP, Molecular Sensing Inc., at SLAS (Society for Laboratory automation and Screening) on January 2013 in Orlando, Florida

Enabling Strengths:
• Most sensitive (pM), molecular interaction platform available; homogeneous and heterogeneous assays; mass and complex matrix independent detection
• Breakthrough in membrane bound protein – ligand interaction characterization
• Overcomes the limitations of SPR & ITC & labeled methods
• Quantitative assay performance with pM LOD sensitivity



Novel GPR39 Agonists: Correlation of Binding Affinity Using Label-Free BSI with Potency In Functional Assays
Daniel Brown1, Niklas Larsson2, Ola Fjellström3, Anders Johansson3, Sara Lundqvist2, Johan Brengdahl2, and Richard J. Isaacs1

1Molecular Sensing, Inc., Nashville, Tennessee, USA,
2AstraZeneca Discovery Sciences, Mölndal, Sweden,
3AstraZeneca CVMD iMED, Mölndal, Sweden

Presented during Discovery on Target 2014


A Label-Free Assay For GPCR Ligand Binding In Free Solution Using Back-Scattering Interferometry
Daniel Brown1, Laura Mizoue2, Karen Gregory2, Meredith Noetzel2, Colleen Niswender2, Jeffery Conn2, and Richard J. Isaacs1

1Molecular Sensing, Inc.
2Vanderbilt University Medical Center, Dept. of Pharmacology

Presented during Discovery on Target on September 2013 at Boston, MA

Presented during NovAliX Conference 2013: Biophysics in Drug Discovery on October 2013 in Strasbourg, France