Protein analysis in heritage materials: from medical to conservation diagnosis with mini-biosensors

Original article: Miniaturized Biosensors to Preserve and Monitor Cultural Heritage: from Medical to Conservation Diagnosis

An important task of a modern conservator is to identify the material composition of an artwork or object. For that reason, a big chunk of the research effort in the field of cultural heritage science is aimed at developing ever more powerful and complex techniques for material analysis. Unfortunately, because of their complexity, these new techniques often require a specialist to carry out the research and interpret the data correctly. Most conservators do not have the resources to make use of the latest developments in modern science for their day-to-day work. In this paper, Giorgia Sciotto and her colleagues have carried out some much-needed work to adapt technologies that might be standard in dedicated analytical laboratories and make them suitable for use by anyone.

The researchers were inspired by cutting-edge medical diagnostic tools to develop a simple immunoassay test that can detect the presence of ovalbumin (from egg) and collagen (from animal glue) proteins. These proteinaceous materials are found as binders (holding paint pigments together), in varnishes, and as glues in paper and book conservation, so their detection and identification is a common pursuit in conservation studios and museums (Figure 1). Traditionally, a conservator could use a microchemical staining method to determine whether a protein was present in a sample. Unfortunately, these traditional methods are not very sensitive; they do not differentiate between types of proteins, and often they end up destroying the precious sample.

Two artworks that contain proteins.
Figure 1: Examples of proteinaceous materials in art. A) A panel painting from the second half of the 15th century that contains animal glue in the gypsum ground and an egg-based finishing layer. B) Detail of a mural painting from 1774 in the Abbey of S. Maria del Monte in which the researchers found animal glue in the pigment layer, possibly due to historical restoration efforts. Circles indicate sampling areas. Reproduced with permission.

The simple sensor designed by Sciotto et al. resembles a common pregnancy test (Figure 2). The only thing a researcher has to do is extract proteins from a sample as small as 0.5 mg, and drop the solution into the sample well. After ten minutes, the ovalbumin and collagen lines can be visually compared with a control sample that contains no proteins; counterintuitively, a loss in intensity indicates the target protein is present in the extract.

Biosensors
Figure 2: A) Picture of the biosensor for the detection of ovalbumin and collagen. B) Schematic overview of the possible outcomes of the test. C) Photographs of actual sensor readings for increasing protein concentrations. OVA = ovalbumin, COL = collagen. Reproduced with permission.

The method makes use of gold nanoparticles (which have a red color) coated with antibodies that selectively bind to either collagen or ovalbumin (Figure 3). As the nanoparticles mix with the sample, there is a competition between binding to the proteins in solution or to the proteins bound on the probe pad. As a result, if there is more protein in the sample, fewer nanoparticles will bind to the pad. With this simple device, the researchers could achieve a limit of detection of 10 µg/mL!

Biosensor mechanism
Figure 3: Working diagram of the biosensor for detection of ovalbumin and collagen. Reproduced with permission.

Sciutto and her colleagues made an effort to reduce the detection limit even further by developing a second, more sensitive sensor. It makes use of a chemiluminescent (light emitting) marker and a relatively affordable CCD camera to detect the presence of target proteins. The adapted method reduced the detection limit by a factor of 100, and it successfully confirmed the presence of animal glue and an egg-white finishing layer in a 15th century panel painting, seen in Figure 1A. However, the added complexity of the chemiluminescent sensor and the additional cost will reduce the general applicability of the method to some extent.

In their conclusions, the researchers share their plans to try and make use of smartphone cameras or other low-cost detectors to carry out measurements and to expand their methodology to detect other biological materials. While this would be a great addition to the restorer’s toolkit, why stop there? Would it be possible to develop cheap one-piece sensors that can distinguish pigments based on specific precipitation or color reactions, or use fluorescent markers for the identification of binding media? Perhaps one day, cheap standard test kits for materials characterization will become available for any practitioner of cultural heritage restoration, whether they work in a large museum or as a private conservator.

2 thoughts on “Protein analysis in heritage materials: from medical to conservation diagnosis with mini-biosensors

  1. Super interesting thanks for the summary….are these sensors in any way able to detect binding media within a cross-sectional sample? I believe I have only come across one article thus far that mentions the use of nanoparticles in this manner. Otherwise we are really left in the dark when it comes to distinguishing original material from restoration material!

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    1. As I understand it, this method requires taking a very small sample and dispersing it in a solvent to extract the proteins. However, this approach is inherently far more sensitive than anything you could do on a cross-section. So I’m afraid it’s a trade-off between minimal sampling and high sensitivity, achieving both remains a challenge…

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