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Mulkerns NMC, Hoffmann WH, Lindsay ID, Gersen H. An Analysis of Semicircular Channel Backscattering Interferometry through Ray Tracing Simulations. SENSORS 2022; 22:s22114301. [PMID: 35684929 PMCID: PMC9185450 DOI: 10.3390/s22114301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 06/02/2022] [Accepted: 06/03/2022] [Indexed: 02/04/2023]
Abstract
Recent backscattering interferometry studies utilise a single channel microfluidic system, typically approximately semicircular in cross-section. Here, we present a complete ray tracing model for on-chip backscattering interferometry with a semicircular cross-section, including the dependence upon polarisation and angle of incidence. The full model is validated and utilised to calculate the expected fringe patterns and sensitivities observed under both normal and oblique angles of incidence. Comparison with experimental data from approximately semicircular channels using the parameters stated shows that they cannot be explained using a semicircular geometry. The disagreement does not impact on the validity of the experimental data, but highlights that the optical mechanisms behind the various modalities of backscattering interferometry would benefit from clarification. From the analysis presented here, we conclude that for reasons of ease of analysis, data quality, and sensitivity for a given radius, capillary-based backscattering interferometry affords numerous benefits over on-chip backscattering interferometry.
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Affiliation(s)
- Niall M. C. Mulkerns
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK; (N.M.C.M.); (W.H.H.); (I.D.L.)
- Bristol Centre for Functional Nanomaterials, University of Bristol, Bristol BS8 1TL, UK
| | - William H. Hoffmann
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK; (N.M.C.M.); (W.H.H.); (I.D.L.)
- Bristol Centre for Functional Nanomaterials, University of Bristol, Bristol BS8 1TL, UK
- School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - Ian D. Lindsay
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK; (N.M.C.M.); (W.H.H.); (I.D.L.)
- Bristol Centre for Functional Nanomaterials, University of Bristol, Bristol BS8 1TL, UK
| | - Henkjan Gersen
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK; (N.M.C.M.); (W.H.H.); (I.D.L.)
- Bristol Centre for Functional Nanomaterials, University of Bristol, Bristol BS8 1TL, UK
- Correspondence:
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2
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Shedding Light on Capillary-Based Backscattering Interferometry. SENSORS 2022; 22:s22062157. [PMID: 35336326 PMCID: PMC8949530 DOI: 10.3390/s22062157] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/02/2022] [Accepted: 03/08/2022] [Indexed: 02/05/2023]
Abstract
Capillary-based backscattering interferometry has been used extensively as a tool to measure molecular binding via interferometric refractive index sensing. Previous studies have analysed the fringe patterns created in the backscatter direction. However, polarisation effects, spatial chirps in the fringe pattern and the practical impact of various approximations, and assumptions in existing models are yet to be fully explored. Here, two independent ray tracing approaches are applied, analysed, contrasted, compared to experimental data, and improved upon by introducing explicit polarisation dependence. In doing so, the significance of the inner diameter, outer diameter, and material of the capillary to the resulting fringe pattern and subsequent analysis are elucidated for the first time. The inner diameter is shown to dictate the fringe pattern seen, and therefore, the effectiveness of any dechirping algorithm, demonstrating that current dechirping methods are only valid for a subset of capillary dimensions. Potential improvements are suggested in order to guide further research, increase sensitivity, and promote wider applicability.
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3
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Eder C, Briesen H. Interferometric Probing of Physical and Chemical Properties of Solutions: Noncontact Investigation of Liquids. Annu Rev Chem Biomol Eng 2022; 13:99-121. [PMID: 35300516 DOI: 10.1146/annurev-chembioeng-092220-123822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Interferometry is a highly versatile tool for probing physical and chemical phenomena. In addition to the benefit of noncontact investigations, even spatially resolved information can be obtained by choosing a suitable setup. This review presents the evolution of the various setups that have evolved since the first interferometers were developed in the mid-nineteenth century and highlights the benefits, limitations, and typical areas of application. This review focuses on interferometry based on electromagnetic waves in the near-infrared and visible range applied to liquid samples, categorizes the chemical/physical properties (e.g., pressure, temperature, composition) and phenomena (e.g., evaporation, crystal growth, diffusion, thermophoresis) that can be assessed, and presents a comprehensive literature review of specific existing applications. Finally, it discusses some fundamental open questions with respect to geometric considerations and overlapping effects. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Cornelia Eder
- Process Systems Engineering, Technical University of Munich, Freising, Germany;
| | - Heiko Briesen
- Process Systems Engineering, Technical University of Munich, Freising, Germany;
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Liang R, Ma G, Jing W, Wang Y, Yang Y, Tao N, Wang S. Charge-Sensitive Optical Detection of Small Molecule Binding Kinetics in Normal Ionic Strength Buffer. ACS Sens 2021; 6:364-370. [PMID: 32842724 DOI: 10.1021/acssensors.0c01063] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Most label-free detection technologies detect the masses of molecules, and their sensitivities thus decrease with molecular weight, making it challenging to detect small molecules. To address this need, we have developed a charge-sensitive optical detection (CSOD) technique, which detects the charge rather than the mass of a molecule with an optical fiber. However, the effective charge of a molecule decreases with the buffer ionic strength. For this reason, the previous CSOD works with diluted buffers, which could affect the measured molecular binding kinetics. Here, we show a technique capable of detecting molecular binding kinetics in normal ionic strength buffers. An H-shaped sample well was developed to increase the current density at the sensing area to compensate the signal loss due to ionic screening at normal ionic strength buffer, while keeping the current density low at the electrodes to minimize the electrode reaction. In addition, agarose gels were used to cover the electrodes to prevent electrode reaction generated bubbles from entering the sensing area. With this new design, we have measured the binding kinetics between G-protein-coupled receptors (GPCRs) and their small molecule ligands in normal buffer. We found that the affinities measured in normal buffer are stronger than those measured in diluted buffer, likely due to the stronger electrostatic repulsion force between the same charged ligands and receptors in the diluted buffer.
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5
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Wan Y, Zhao J, He J, Lou X. Nano-Affi: a solution-phase, label-free, colorimetric aptamer affinity assay based on binding-inhibited aggregation of gold nanoparticles. Analyst 2020; 145:4276-4282. [DOI: 10.1039/d0an00827c] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The ideal way to assess aptamer affinity is when both aptamer and target are in a native state, without the unpredictable interference associated with labelling and surface immobilization.
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Affiliation(s)
- Yuan Wan
- Department of Chemistry
- Capital Normal University
- Beijing
- China
| | - Jiaxing Zhao
- Department of Chemistry
- Capital Normal University
- Beijing
- China
| | - Junlin He
- State Key Laboratory of Toxicology and Medical Countermeasures
- Beijing Institute of Pharmacology and Toxicology
- Beijing
- China
| | - Xinhui Lou
- Department of Chemistry
- Capital Normal University
- Beijing
- China
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6
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Real-Time Interferometric Refractive Index Change Measurement for the Direct Detection of Enzymatic Reactions and the Determination of Enzyme Kinetics. SENSORS 2019; 19:s19030539. [PMID: 30696020 PMCID: PMC6387378 DOI: 10.3390/s19030539] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Revised: 01/18/2019] [Accepted: 01/22/2019] [Indexed: 12/03/2022]
Abstract
Back scatter interferometry (BSI) is a sensitive method for detecting changes in the bulk refractive index of a solution in a microfluidic system. Here we demonstrate that BSI can be used to directly detect enzymatic reactions and, for the first time, derive kinetic parameters. While many methods in biomedical assays rely on detectable biproducts to produce a signal, direct detection is possible if the substrate or the product exert distinct differences in their specific refractive index so that the total refractive index changes during the enzymatic reaction. In this study, both the conversion of glucose to glucose-6-phosphate, catalyzed by hexokinase, and the conversion of adenosine-triphosphate to adenosine di-phosphate and mono-phosphate, catalyzed by apyrase, were monitored by BSI. When adding hexokinase to glucose solutions containing adenosine-triphosphate, the conversion can be directly followed by BSI, which shows the increasing refractive index and a final plateau corresponding to the particular concentration. From the initial reaction velocities, KM was found to be 0.33 mM using Michaelis–Menten kinetics. The experiments with apyrase indicate that the refractive index also depends on the presence of various ions that must be taken into account when using this technique. This study clearly demonstrates that measuring changes in the refractive index can be used for the direct determination of substrate concentrations and enzyme kinetics.
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Dunn RC. Wavelength Modulated Back-Scatter Interferometry for Universal, On-Column Refractive Index Detection in Picoliter Volumes. Anal Chem 2018; 90:6789-6795. [PMID: 29762009 DOI: 10.1021/acs.analchem.8b00771] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Wavelength-modulated back scatter interferometry (M-BSI) is shown to improve the detection metrics for refractive index (RI) sensing in microseparations. In M-BSI, the output of a tunable diode laser is focused into the detection zone of a separation channel as the excitation wavelength is rapidly modulated. This spatially modulates the observed interference pattern, which is measured in the backscattered direction. Phase-sensitive detection using a split photodiode detector aligned on one fringe of the interference pattern is used to monitor RI changes as analytes are separated. Using sucrose standards, we report a detection limit of 700 μg/L in a 75 μm i.d. capillary at the 3σ level, corresponding to a detection volume of 90 pL. To validate the approach for electrophoretic separations, Na+ and Li+ were separated and detected with M-BSI and indirect-UV absorbance on the same capillary. A 4 mg/L NaCl and LiCl mixture leads to comparable separation efficiencies in the two detection schemes, with better signal-to-noise in the M-BSI detection, but less baseline stability. The latter arises in part from Joule heating, which influences RI measurements through the thermo-optic properties of the run buffer. To reduce this effect, a 25 μm i.d. capillary combined with active temperature control was used to detect the separation of sucrose, glucose, and lactose with M-BSI. The lack of suitable UV chromophores makes these analytes challenging to detect directly in ultrasmall volumes. Using a 55 mM NaOH run buffer, M-BSI is shown to detect the separation of a mixture of 174 mg/L sucrose, 97 mg/L glucose, and 172 mg/L lactose in a 15 pL detection volume. The universal on-column detection in ultrasmall volumes adds new capabilities for microanalysis platforms, while potentially reducing the footprint and costs of these systems.
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Affiliation(s)
- Robert C Dunn
- Ralph N. Adams Institute for Bioanalytical Chemistry , University of Kansas , 2030 Becker Drive , Lawrence , Kansas 66047 , United States
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Laser interferometry of the hydrolytic changes in protein solutions: the refractive index and hydration shells. J Biol Phys 2018; 44:345-360. [PMID: 29752596 DOI: 10.1007/s10867-018-9494-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 03/29/2018] [Indexed: 10/16/2022] Open
Abstract
Using an original laser interferometer of enhanced sensitivity, an increase in the refractive index of a protein solution was observed during the reaction of proteolysis catalyzed by pepsin. The increase in the refractive index of the protein solution at a concentration of 4 mg/ml was [Formula: see text] for bovine serum albumin and [Formula: see text] for lysozyme. The observed effect disproves the existing idea that the refractive index of protein solutions is determined only by their amino acid composition and concentration. It is shown that the refractive index also depends on the state of protein fragmentation. A mathematical model of proteolysis and a real-time method for estimating the state of protein hydration based on the measurement of refractive index during the reaction are proposed. A good agreement between the experimental and calculated time dependences of the refractive index shows that the growth of the surface of protein fragments and the change in the number of hydration cavities during proteolysis can be responsible for the observed effect.
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Baksh MM, Finn M. An experimental check of backscattering interferometry. SENSORS AND ACTUATORS. B, CHEMICAL 2017; 243:977-981. [PMID: 28529409 PMCID: PMC5433263 DOI: 10.1016/j.snb.2016.12.055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Backscattering interferometry (BSI) was used to determine the association constants for four well-known biomolecular interactions: protein A + IgG, trypsin + antitrypsin, trypsin + p-aminobenzamidine, and antithrombin + heparin. Each gave well-defined binding curves and Kd values in close agreement with published findings obtained using other techniques. These results stand in direct contrast to the claims in a 2015 publication in this journal (Discussion of "Back Scattering Interferometry revisited-a theoretical and experimental investigation" Jørgensen, T.M.; Jepsen, S.T.; Sørensen, H.S.; di Gennaro, A.K.; Kristensen, S.R. Sensors and Actuators B 2015, 220, 1328-1337, doi: 10.1016/j.snb.2015.06.121), thus invalidating the claim that BSI is unable to make measurements of this kind. The experimental details are discussed, and several potential sources of error in the previous publication are identified. No comments are made here on the discussion of the theoretical aspects of the BSI technique.
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Article does not explain the origin of free-solution protein interaction signals. Proc Natl Acad Sci U S A 2016; 113:E4930. [PMID: 27462112 DOI: 10.1073/pnas.1608094113] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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11
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Reply to Varma: Elucidation of the signal origin for label-free, free-solution interactions. Proc Natl Acad Sci U S A 2016; 113:E4931-2. [PMID: 27462104 DOI: 10.1073/pnas.1609553113] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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12
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Origin and prediction of free-solution interaction studies performed label-free. Proc Natl Acad Sci U S A 2016; 113:E1595-604. [PMID: 26960999 DOI: 10.1073/pnas.1515706113] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Interaction/reaction assays have led to significant scientific discoveries in the biochemical, medical, and chemical disciplines. Several fundamental driving forces form the basis of intermolecular and intramolecular interactions in chemical and biochemical systems (London dispersion, hydrogen bonding, hydrophobic, and electrostatic), and in the past three decades the sophistication and power of techniques to interrogate these processes has developed at an unprecedented rate. In particular, label-free methods have flourished, such as NMR, mass spectrometry (MS), surface plasmon resonance (SPR), biolayer interferometry (BLI), and backscattering interferometry (BSI), which can facilitate assays without altering the participating components. The shortcoming of most refractive index (RI)-based label-free methods such as BLI and SPR is the requirement to tether one of the interaction entities to a sensor surface. This is not the case for BSI. Here, our hypothesis is that the signal origin for free-solution, label-free determinations can be attributed to conformation and hydration-induced changes in the solution RI. We propose a model for the free-solution response function (FreeSRF) and show that, when quality bound and unbound structural data are available, FreeSRF correlates well with the experiment (R(2)> 0.99, Spearman rank correlation coefficients >0.9) and the model is predictive within ∼15% of the experimental binding signal. It is also demonstrated that a simple mass-weighted dη/dC response function is the incorrect equation to determine that the change in RI is produced by binding or folding event in free solution.
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