Digital Sample Prep

As many of you will already know, three-dimensional (3D) printing is a broad term that describes a production process that combines computer aided design (CAD) with innovative techniques and diverse starting materials to creates objects of various shapes and geometries. Most 3D printing uses layer-by-layer deposition of suitable materials – including organic polymers, ceramics, and metals – to create the final product, which is why the term “additive manufacturing” is also used to describe the same process.

First introduced in the 1980s, 3D printing is relatively new technology, but it has already been successfully adopted in various scientific fields. Medicine, dentistry, veterinary science, biology and chemistry have all taken advantage of its versatile manufacturing capability. And with 35 years of further advances and applications under its belt, it has reached a stage where it is mature enough to become a mainstream manufacturing process in many more areas.

Stereolithography (SLA) is one popular 3D printing technology, but there are others: fused deposition modeling (FDM, based on the consecutive layering of softened/melted thermoplastic materials), selective laser sintering (SLS), as well as inkjet and PolyJet. The selection of the technology used largely depends on the requirements of the final printed object in terms of material biocompatibility, strength, composition, surface roughness, and dimensions, for example. Whichever technology is used, all 3D printing processes begin with the modeling of a 3D object using CAD software. The CAD model is saved as a file (for example, an .STL file for stereolithography), and can be interpreted by any suitable 3D printer.

Analytical chemistry – a demanding field in terms of reproducibility – has recently started to benefit from the increasingly accurate ability of 3D printing to rapidly construct a variety of scaffolds and platforms. Electrophoresis devices, flow-cells for chemiluminescence detectors, or injection valves for flow systems that can be coupled with sophisticated analytical instruments as for example with ICP-MS are among the various tools reported so far in literature (1)(2).

The ability to manufacture reproducible and complex scaffolds (at low cost, in many cases) is specifically suited to the preparation of sample preparation materials. 3D-printed electrodes are one widely available platform, but printed membranes with biorecognition elements are expected to gain more attention in the future. With regards to solid phase extraction (SPE) – one of the most broadly used approaches for sample preparation – 3D printing can be used to integrate flow-through devices and SPE capability into a single unit. And because such devices are produced from a computer template and recreated accurately by 3D printing, files encoding the best performers (or even those devices with promise) can easily be shared between researchers and labs across the world, allowing for further iterative improvements – and giving everyone access to sample preparation advances (3)(4).

Current examples of SPE applications of 3D printing include the production of devices for “multisyringe flow injection analysis” (MSFIA), which automates SPE across various sorbents, including packed beds, magnetic particles, stir bars and disks (5). Three-dimensional printed devices have also been used to automate pre-SPE and post-SPE integrated sample preparation for the preconcentration and further determination of metals, such as lead and iron, in water samples (6)(7).

SPE columns or cartridges constructed using 3D printing techniques can integrate multiple components such as, for example, various hormones, and provide supplementary functionality and improved performance over conventional SPE formats. The potential benefits? i) pre-concentration can take place with high extraction efficiency, accuracy and precision, ii) matrix interferences can be reduced because of high tolerance to salt matrices  and iii) high sample loading flow rates can reduce interference, facilitating highly sensitive determination of trace elements in environmental samples (1)(4)(7).

Recently, molecularly imprinted polymer (MIP)-functionalized scaffolds were proposed as novel SPE sorbents for the extraction of a psychoactive drug (8).  Such tailor-made scaffolds can be 3D printed in a relatively straightforward way to meet the exact shape and geometry of a defined SPE column. Would it be possible to apply the same approach to a multi-analyte application; for example, by integrating several such MIP-functionalized scaffolds (each targeted to a specific analyte) into a single SPE column? If so, such novel SPE sorbents could find their way into food and clinical analysis, too.

I consider 3D printed SPE sorbents to be a milestone in the field of chemical analysis, but the application of additive manufacturing is not limited to SPE. It can be applied in other novel ways; one good example being “on-line carbon nanofiber reinforced hollow fiber-mediated liquid phase microextraction” – a 3D-printed extraction platform that serves as a “front end” to the liquid chromatograph, allowing automatic sample preparation (9).

In short, 3D printing is an exciting trend that could potentially lead to increased efficiency and miniaturization in analytical applications. Devices tailored to specific analytical needs allow us to experiment with an entirely new – and continually expanding and changing – toolkit. How fast can we move forward? Well, that very much depends on how quickly the wider analytical science community embraces both the technology – and the potential – of 3D printing.