# The Detection of Long-Chain Bio-Markers Using Atomic Force Microscopy
## 4 Discussion  
The uniqueness of the force detachment signal for long chain organic polymers on mineral surfaces will now be considered. A potential interference could be from inorganic molecules that are linear, long chain, flexible, polymeric strands present in a mineral matrix. However there are very few naturally occurring inorganic materials with these properties. The most common naturally occurring, linear chain, inorganic polymer is elemental sulfur. However, below the melting point (114 \({}^{\circ}\)C) polymeric sulfur is unstable and forms of rhombic S\({}_{8}\)[21]. Contamination is a problem with all trace organic detection methods. This is particularly true for the analysis of fossils or for detecting organics using spacecraft instruments. Experiments applying this new method for detecting long-chain bio-molecules need to include controls and sample blanks to assure organic residues were not added to the sample during collection. The use of AFM-FS to study biomolecules that are not chemically attached (tethered) to a surface is a new approach that is useful for studying bio-molecules on fossils or planetary mineral surfaces. The distinctive molecular detachment signal adds a new feature for detecting signs life or pre-biotic compounds. The use of atomic force microscopy to analyze mineral surfaces for organic residues and long-chain bio-polymers has been demonstrated. A variety of long chain polymers on mineral surfaces have been analyzed. This includes spore surface proteins, algae and fossils containing known bio-organic residue. AFM force spectroscopy produces a unique force-curve that is indicative of the presence of polymer chains. This is quite distinct from abiotic mineral surfaces. This approach may be incorporated with other methods for additional chemical information. The tip-enhanced infrared spectroscopy of removed residues provides additional chemical information. It should be noted that a similar application of tip-enhanced Raman spectroscopy could be used to provide electrochemical analysis [22]. The detection of the chemical signatures of life is a challenge for both in situ planetary exploration and for the analysis of terrestrial fossils [6]. Many schemes have been proposed ranging from the detection of specific chemistry found in terrestrial life to measuring general characteristics such as molecular chirality. A goal is to find markers for biological activity that are general enough without being obscured by abiotic background chemistry. Claims about detecting life or pre-biotic molecules in  
Figure 5: The infrared spectrum of the organic material from the fossil collected onto the AFM tip. This shows a mixture of bio-organic functional groups including hydrocarbon, esters, and amides. the oldest fossils, meteorites or in planetary environments are inherently controversial and require multiple levels of proof. Obviously, no single approach is definitive. The new method presented here is extremely sensitive (single molecule detection) and is relatively non-destructive so it may operate in a suite of other analytical methods. AFM instruments have flown on two space missions, the Phoenix MECA experiment and the Rosetta MIDAS experiment. The implementation of AFM instruments equipped with force spectroscopy on future spacecraft missions may use existing designs with relatively minor modifications of the software to enable force spectroscopy measurements. This work demonstrates a new application of the AFM that is relevant to astrobiology missions. Lastly, this type of analysis in a laboratory setting could be useful for the analysis of fossils or meteorites. The work described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, through an agreement with the National Aeronautics and Space Administration, California Institute of Technology. Government sponsorship acknowledged (c) 2019 California Institute of Technology. I would like to thank [PERSON] for providing the stromatolite sample. The author declares no conflict of interest.