Screen Printed Particle-Based Microfluidics: Optimization and Exemplary Application for Heavy Metals Analysis.

In this work, a screen-printing method was developed to create porous particle-based materials as layers with specifically designed shape to produce microfluidics systems. Among several tested binding agents, xanthan gum was found to be an excellent choice for a printing mixture thickener as well as a durable binder for the resulting material. In addition to demonstrating control over the shape of the printed microfluidics chips, control over material thickness, wetting characteristics and general method accuracy were also investigated. The applicability of the introduced method was further demonstrated with a development of an exemplary microfluidics chip for quantitative detection of Fe (III), Ni (II), Cu (II), Cd (II), and Pb (II) from a mixed sample at millimolar levels. The novel approaches demonstrated in this article offer new perspective into creating multiplexed on-site chemical analysis tests.

A New Direction in Microfluidics: Printed Porous Materials.

In this work, the feasibility of a novel direction for microfluidics is studied by demonstrating a set of new methods to fabricate microfluidic systems. Similarly to microfluidic paper-based analytical devices, porous materials are being used. However, alternative porous materials and different printing methods are used here to give the material the necessary pattern to act as a microfluidic system. In this work, microfluidic systems were produced by the following three separate methods: (1) by curing a porous monolithic polymer sheet into a necessary pattern with photolithography, (2) by screen printing silica gel particles with gypsum, and (3) by dispensing silica gel particles with polyvinyl acetate binder using a modified 3D printer. Different parameters of the printed chips were determined (strength of the printed material, printing accuracy, printed material height, wetting characteristics, repeatability) to evaluate whether the printed chips were suitable for use in microfluidics. All three approaches were found to be suitable, and therefore the novel approach to microfluidics was successfully demonstrated.

Sacrificial Layer Technique for Releasing Metallized Multilayer SU-8 Devices.

The low fabrication cost of SU-8-based devices has opened the fields of point-of-care devices (POC), µTAS and Lab-on-Chip technologies, which call for cheap and disposable devices. Often this translates to free-standing, suspended devices and a reusable carrier wafer. This necessitates a sacrificial layer to release the devices from the substrates. Both inorganic (metals and oxides) and organic materials (polymers) have been used as sacrificial materials, but they fall short for fabrication and releasing multilayer SU-8 devices. We propose photoresist AZ 15nXT (MicroChemicals GmbH, Ulm, Germany) to be used as a sacrificial layer. AZ 15nXT is stable during SU-8 processing, making it suitable for fabricating free-standing multilayer devices. We show two methods for cross-linking AZ 15nXT for stable sacrificial layers and three routes for sacrificial release of the multilayer SU-8 devices. We demonstrate the capability of our release processes by fabrication of a three-layer free-standing microfluidic electrospray ionization (ESI) chip and a free-standing multilayer device with electrodes in a microchannel.

Utilization of data below the analytical limit of quantitation in pharmacokinetic analysis and modeling: promoting interdisciplinary debate.

Traditionally, bioanalytical laboratories do not report actual concentrations for samples with results below the LOQ (BLQ) in pharmacokinetic studies. BLQ values are outside the method calibration range established during validation and no data are available to support the reliability of these values. However, ignoring BLQ data can contribute to bias and imprecision in model-based pharmacokinetic analyses. From this perspective, routine use of BLQ data would be advantageous. We would like to initiate an interdisciplinary debate on this important topic by summarizing the current concepts and use of BLQ data by regulators, pharmacometricians and bioanalysts. Through introducing the limit of detection and evaluating its variability, BLQ data could be released and utilized appropriately for pharmacokinetic research.

Sponge Spray-Reaching New Dimensions of Direct Sampling and Analysis by MS.

Sample preparation for the analysis of clinical samples with the mass spectrometer (MS) can be extensive and expensive. Simplifying and speeding up the process would be very beneficial. This paper reports sponge spray-a novel sampling and direct MS analysis approach-attempting exactly that. It enables direct analysis without any sample preparation from dried blood, plasma, and urine. The tip of a volumetric absorptive microsampling device is used to collect an exact amount of sample and from that same tip an electrospray can be directed into a mass spectrometer. We demonstrate here that, although with significant matrix effects, quantitation of penicillin G, a common antimicrobial, is possible in plasma and in urine, with essentially no sample preparation.

Tutorial on estimating the limit of detection using LC-MS analysis, part I: Theoretical review.

A large body of literature exists on the limit of detection (LOD), but there is still a lot of confusion about this important validation parameter. This confusion mainly stems from its statistically complex background. The goal of this two-part tutorial is to discuss and clarify the topic of LOD for practitioners. The two main conclusions of this tutorial are: (1) the choice of how to estimate LOD should be based on the purpose of the analytical method that is being validated (e.g. considerable effort should not be made to estimate LOD for a method that is not used for detecting traces in the vicinity of LOD), and (2) LOD estimates are strongly dependent on different assumptions and the approach used, and therefore caution must be exercised when using the estimate or when comparing different estimates. Part I of the tutorial contains a theoretical discussion (without excessively sophisticated statistics) and part II contains examples based on experimental data. In Part I, LOD and other definitions related to it are reviewed, and their estimation and use are discussed. The assumptions and practicality of different approaches to estimate LOD are compared. Different aspects of the analytical method that strongly influence LOD estimates (e.g. linearity, scedasticity and day-to-day variability of LOD) together with experimental design considerations when estimating LOD are discussed. In part II, LOD is estimated for the LC-MS/MS analysis method to detect pesticides on separate days. The performance of different tests on the data necessary for LOD estimation are discussed and the results of different approaches under review in this tutorial are compared. In conclusion, a decision tree is proposed for estimating and monitoring LOD. A detailed working procedure for estimating LOD is presented. Several topics are pointed out in which further research and discussion is needed.

Tutorial on estimating the limit of detection using LC-MS analysis, part II: Practical aspects.

In part II of this tutorial, the investigated approaches of estimating the limit of detection (LOD) are applied to experimental data from LC-MS measurements. Important practical aspects specific to LC-MS and related to LOD are reviewed. The results of different tests of estimating linearity and scedasticity are compared. LOD estimates obtained with different approaches (for both simple characterization of the analysis method and accurate interpretation of the results) are applied to the data and the obtained values are compared. As a conclusion, a decision tree is proposed for estimating LOD for analytical methods using the LC-MS technique.

Tutorial review on validation of liquid chromatography-mass spectrometry methods: part II.

This is the part II of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC-MS) and discuss specific issues that arise with MS (and MS-MS) detection in LC (as opposed to the "conventional" detectors). The Part II starts with briefly introducing the main quantitation methods and then addresses the performance related to quantification: linearity of signal, sensitivity, precision, trueness, accuracy, stability and measurement uncertainty. The last section is devoted to practical considerations in validation. With every performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to handle it, specifically in the case of LC-MS methods.

Tutorial review on validation of liquid chromatography-mass spectrometry methods: part I.

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC-MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the "conventional" detectors). The Part I briefly introduces the principles of operation of LC-MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC-MS methods.