Electrical Sensing Zone / Microfluidic Resistive Pulse Sensing

Method Introduction

Electrical Sensing Zone (ESZ), also known as (microfluidic) resistive pulse sensing ((M)RPS), is a non-light-based technique for sizing and counting particles in the nm- and µm-size range.

ESZ/MRPS works by applying an electrical field between opposite sides of an orifice. Particles suspended in a conductive electrolyte solution are aspirated through the orifice and, upon passage, increase the electrical resistance proportional to the volume of their non-conductive part (Coulter principle). Size determination is based on calibration with spherical sizing standards and provides an equivalent spherical diameter of the analyzed particles. Depending on the system and setup, particles from about 50 nm up to 1 mm can be measured.

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  1. Grabarek AD, Weinbuch D, Jiskoot W, Hawe A., Critical Evaluation of Microfluidic Resistive Pulse Sensing for Quantification and Sizing of Nanometer- and Micrometer-Sized Particles in Biopharmaceutical Products, J Pharm Sci. 2019 Jan

Applications

On the one hand, ESZ/MRPS is used as an early research tool in combination with nanoparticle tracking analysis (NTA) and dynamic light scattering (DLS). When measuring in this low size range, the most significant benefit is the need for very low sample volumes of only a few µL. On the other hand, ESZ/MRPS is used as an orthogonal technique to validate results from light-based particle characterization techniques in the nanometer and visible size range, such as flow imaging microscopy (FIM) and light obscuration (LO). The need for large sample volumes in the upper size range restricts the technique’s application during formulation development and stability studies.

ESZ/MRPS additionally requires a minimum sample conductivity, which in some instances requires the addition of electrolytes. ESZ/MRPS is suitable for analyzing protein aggregates, particles and colloidal systems, such as virus-like particles and polymers.

Quality and Biosafety Level

We provide all our analytical services with the highest quality standards. Experienced scientists carry out each project, and a scientific reviewer comprehensively checks every report or data presentation.

We offer this technology with the following quality and biosafety levels:

R&D level

We offer this method under R&D. Our GRP system assures the highest-quality research standards.

Up to biosafety level 1

This method can be applied to proteins, nucleic acids, and most viral vectors, including AAVs and more.

Analytical Method Development, Qualification and Validation

For common sample types, we can often apply standardized methods with little setup effort. However, when needed, our experienced analytical experts create or optimize custom methods tailored to your active pharmaceutical ingredient, product type and development phase.

Method Development

Our method development approach tailors sample preparation, method settings and data analysis to the needs of your project and sample.

We include representative samples and, where available, suitable reference standards and stressed/degraded materials, allowing our analytical scientists to design a highly suitable, stability-indicating, robust and repeatable method. Upon request, we will compile a detailed description of the method for your records.

Method Qualification

Method qualification is the initial assessment of an analytical procedure’s performance to show its suitability for its intended purpose.

During method qualification, our analytical scientists perform documented testing demonstrating that the analytical procedure meets criteria in several categories. Criteria may include factors such as repeatability, specificity and robustness. We compile a qualification plan and report, including all relevant data.

Method Validation

Under GMP conditions, method validation confirms that an analytical procedure’s performance suits its intended purpose. Depending on the method’s scope, a broad range of method characteristics, such as specificity, accuracy, precision, limit of detection/limit of quantification (LOD/LOQ), linearity and range, is considered.

During method validation, our analytical scientists perform documented testing demonstrating that the analytical procedure consistently produces a result that meets the predetermined acceptance criteria. We compile a validation plan and report that includes all relevant data.

Depending on the development phase, a fit-for-purpose validation approach can be offered, adjusting the validation required efforts in a phase-appropriate way to meet the method’s needs.

Method Verification

Compendial method verification confirms that a compendial method (e.g., from Ph. Eur. or USP) is suitable and reliable for its intended purpose under the specific conditions of the laboratory.

Unlike full method validation, compendial method verification is often considered a partial validation since the method has already undergone extensive testing and validation during its inclusion in the compendium. The extent of method verification depends on the type of method.

During method verification, our analytical scientists perform documented testing demonstrating that the developed analytical method performs adequately for the specific product or matrix being tested and within the specific laboratory where the method will be employed.

Talk to Our Experts or Request a Quote

Our expert team is ready to answer your questions and guide you to the services best suited to your program’s modality, stage and challenge. If your needs are well-defined, we’ll begin the quotation process.

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