Raman Ponderings

Fran Adar - July, 2008

We all agree that Raman technology has undergone fundamental changes since 1990 when the notch filter was introduced. What does that imply about who is using the equipment and where future growth will be? For sure there are many manufacturing problems that are being addressed, with identification of defects and contaminants being in the upper tier. Other things are happening as well: In the semiconductor field, IC manufacturers are monitoring “cross-hatched” strain in SiGe layers on silicon which will affect the performance of devices. But, while this is an important application, not many instruments will be acquired to do this measurement. Multiple instruments are being sold into chemical manufacturing sites, and we are hoping to see an entry from Kaiser, who is currently the leader in this field. A number of Raman microscopes have been placed in the laboratories of art museums for conservation of cultural heritage (and the identification of forgeries), but growth here is also expected to be limited.

So if there is going to be explosive growth in terms of numbers of instruments placed, where would one expect that to occur? Many people have been looking to the medical area. There is certainly reason to believe that this is possible. The quality of information available from a Raman spectrum is potentially quite high. There are at least tens of academic groups actively using Raman to study disease processes, with a goal of being predictive. But nothing has become robust enough to achieve credibility in the medical community and to be commercialized. What are the hurdles, and can this happen? One of the biggest hurdles is in the optical sampling. The diagnostician and surgeon would like an endoscopic probe. Several have been designed and tested, and patents have been applied for. Genomic and proteomic applications would not require such probes; automated measurements of sample arrays would be easy with current instruments and software. My guess is that genomic arrays would be most easily done using SERS technology, because there are already labs that are labeling DNA fragments with gold particles. Proteomics might not be as well addressed by SERS because of the limited amounts of aromatic groups in the peptides. But an array of droplets could be deposited on hydrophobic substrates which serve to provide concentrated deposits of pure materials which can be differentiated using multivariate analysis techniques (MVA). After the measurements have been made, the next hurdle is the achieving predictability. Large numbers of patients need to be studied in order to assemble reliable statistics. The MVA techniques are fairly well developed, and are being applied by the academics working on these problems.

Will Raman become a household word in any bioclinical area? Unfortunately I am not a good predictor. But I can say that everything is in place for this to happen, including the national funding of academics that will drive it to happen. I think that if someone solves a clinical problem with Raman that is waiting for a solution, then the credibility of Raman in the medical community will go up, and things may happen more quickly.

The other area to look for possible growth would be Homeland Security. In fact, thing have been happening here. We know that tens of portable FTIR instruments per week are going out for these applications, and that there are Raman players in this area as well. As the cost of Raman microscopes and portable systems continues to drop many more forensic scientists will start using Raman to help solve crimes. There is also the taking advantage of the increased sensitivity of SERS to boost the detectability to interesting levels. I actually discussed this in a recent column in Spectroscopy magazine. Here the challenge is to make the SERS-active substrate or particles reproducible – the Holy Grail of SERS. This is close to being a reality, but it would be great to hear from workers active in the field.

Agree or disagree? Let us know what you think. Go to the Forum section, challenge me and tell me what I don’t know. It should be fun.