Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been used for real-world applications ranging from mining sample analysis to threat analysis to industrial process control. Participants in this Technology Forum are Benjamin W. Smith of the University of Florida, Andrzej Miziolek of the US Army Research Laboratory, and Steve Buckley of Photon Machines, Inc.

There has been much activity in LIBS research over the past 20 years and as lasers and detectors become better and less expensive, the instrumentation for LIBS is becoming more accessible to users in government and industry. What will it take to move LIBS from the research lab into the operational analytical lab?

Smith: LIBS will have a difficult time finding a routine place in the suite of analytical methods used in the analytical laboratory. ICP emission and mass spectrometric methods provide vastly superior precision and accuracy over a very wide range of concentrations. The significant advantages of LIBS are rapidity and the ability for in-situ measurements directly on solids and for the time being the applications that require these are not in the laboratory but in industrial process control. That is where LIBS will find its most useful application.

Miziolek: This transition from “research on LIBS” to “analysis using LIBS” has already started to take place. This is especially true for certain industrial operational analytical labs which specialize in analysis of materials such as molten glass, molten steel and aluminum, and various ores. Generally, these types of specific industrial applications are not widely known due to competitive advantage considerations.

With regard to taking the next step and bringing LIBS devices into the field, away from a lab environment, there are also some examples such as in mining operations. The additional step of having man-portable LIBS devices that are battery operated is just now starting. Having said that, the components used in LIBS, particularly the lasers, are still not generally well-suited to LIBS, especially for the growing number of LIBS applications that are based on single-shot analysis using burst mode. Current lasers are overengineered with larger size, weight, and cost than need to be if the lasers were built for burst-mode operation. New lasers are coming on the horizon, especially driven by the increasing awareness that the market for these devices is substantial, specifically for field applications in security, protection, environmental, and geological studies.

The core LIBS attributes of real-time analysis, no sample preparation, high sensitivity, and high specificity, not to mention the fact that the modern LIBS devices (broadband, high resolution) are capable of detecting all elements in the sample at parts-per-million level or higher per each laser shot, make a strong argument toward the utility and desirability of this kind of technology for real-world applications.

Buckley: In my view, LIBS is already moving into the operational analytical laboratory. We have numerous examples of products that are successfully being used in analytical labs in major corporations in several major industries. The typical industrial user in today’s market would still be characterized as a “leader” in his or her field – LIBS has not hit the mainstream industrial market by any stretch of the imagination. Given the state of the hardware and software as we see it, this is just a matter of time.

What are the "killer apps" that LIBS is best positioned to address within analytical chemistry?

Smith: The optimal applications for LIBS will capitalize upon the inherent strengths: rapidity and in-situ measurements. Moreover, they will rely upon the excellent, rich qualitative information that LIBS provides rather than the modest quantitative data. LIBS is perfectly suited for rapid sorting tasks such as treated and nontreated wood waste, scrap metal identification and sorting, process monitoring and quality control. It will also find uses for rapid semiquantitative survey measurements such as heavy metals in soils and quick identification of minerals in the field.

Miziolek: My definition of "killer app" is one that has significance in either the importance of its impact on humankind, both civilian and military (for example, rapid pathogen analysis for public health); involves a lot of money (like gem analysis); has impact on a significant percentage of the population (for example, improved lead detection or identification of source of building materials); does something so well where there is a big market so that thousands of units are sold; or all of the above.

With this definition in mind, LIBS technology is not quite there yet with proven examples of “killer apps.” However, we clearly see a number of “killer apps” just around the corner. I will mention just a few.

• Biomedical: A recent review article cites nearly 90 references relating to LIBS as applied to biomedical applications. This includes dental–mineralized tissues, soft tissues, as well as pathogen–bacteria identification. One very significant application is to rapidly identify worrisome “superbugs” (such as MRSA) in a hospital setting. Some papers have cited the use of LIBS for detecting cancerous cells on the basis of significant changes in the inorganic components relative to healthy cells. Imagine the use of a clinical LIBS device for real-time in-vivo analysis of lumps that are suspected during routine mammography check-ups. A rapidly growing body of literature is demonstrating the excellent ability of LIBS to identify specific bacteria, down to the strain level. Imagine a LIBS device in a clinic or hospital that can identify a suspected pathogen during a 15-minute doctor’s office visit. From what we have seen so far, I would consider the biomedical application as a “super-killer app.”
• Forensics/provenancing: In the last few years there have been a number of publications that describe excellent performance of LIBS for forensics and materials matching applications. Forensics applications include glass, fabric, ink, paper, and soils analysis. In materials matching and source identification (provenancing) there are publications that report the LIBS ability to identify the geological source of rocks and the specific mines that certain gems have come from (because of elemental fingerprinting). LIBS devices are expected to become important in the gem trade world, especially as fake gems are becoming harder to spot.
• First responders: Since LIBS has an unusual ability to detect and identify a wide range of threat and hazardous materials, it appears to be an excellent candidate for first responder use worldwide, for both military and civilian applications. If size and cost of the LIBS devices drop sufficiently, then the worldwide market for first responders will be in the tens of thousands of units.
• Environmental: A field-portable LIBS device that can provide a real-time analysis of various environmental samples in the field would be very valuable, especially during either natural or man-made disasters. Again, the size, weight, cost, and user-friendliness will be key in defining how big of a “killer app” this may be.

Buckley: The best applications for LIBS play to the strengths of the method: real-time analysis with little sample preparation, measurement of light elements, and the ability to do depth profiling and surface mapping. No other method can claim two or more of these strengths simultaneously — and thus our most happy customers typically have applications fitting two or more of these strengths, and LIBS is the answer to a longstanding analysis problem. There is also the need for exploratory multielement analysis that LIBS can fulfill quite nicely. We have one customer in particular who is incorporating LIBS into a rapid analysis suite that their corporate analytical lab is developing.

What are the key advantages and challenges related to LIBS as an analytical tool?

Smith: The key advantages remain rapidity, rich information content and in-situ measurement capability but one can also add to this an inherent instrumental robustness. LIBS instruments can be well suited to use in the field and in adverse environments. The dominant challenge to increased applicability is still quantitative analysis. The key issues related to quantitation are the very small sample mass, the sensitivity of the sampled mass to sample morphology and laser-material interactions. There also remains a general lack of suitable solid standard reference materials but this is a problem for all methods that involve direct solids analysis. Successful applications are being made — for example, the determination of carbon in steels — but these result from concerted research effort toward very focused and particular problems.

Miziolek: Advantages such as speed, sensitivity, specificity, ease-of-use have already been mentioned. Versatility in form factor is another key point where you can have LIBS systems that are close-contact, proximity contact, standoff, robotics-mounted, and even underwater capable, which significantly opens up the world of possible applications. Versatility in the wide number of materials that can be analyzed is also extraordinary. LIBS is arguably the most versatile threat analyzer being capable of analyzing all five out of five threats (chemical, biological, radiological, nuclear, and explosives [CBRNE]) using the same device, but with the caveat that the sample has to be presented line-of-sight to the laser. Having said that, the challenges will continue to be in the area of quantification, which is not easy but is done frequently with the use of calibration standards and matrix matching, as well as practical considerations such as size, weight, cost, and where applicable, eye-safety. Simply put, the power and strength of the LIBS technology can be summarized by the famous quote, “it’s elementary my dear Watson.”

Buckley: The real advantages are related to the strengths of the method I outlined above. The challenge is making the multistep ablation plus plasma emission simple and repeatable. Understanding both the ablation process and the plasma emission is a real key to success, and helps our efforts here immensely. There is enough physics and chemistry in a typical LIBS measurement to satisfy the thesis requirements of hundreds more thesis for graduate students. Success occurs when that complexity can be tamed and harnessed to provide usable and repeatable results for the analyst. This typically requires folding application knowledge into the LIBS solution.