*Cybersecurity*

Lastly, the use of biosensors for cybersecurity is a growing trend. The use of sensors for authentication of an individual and a novel methodology related to cryptography were recently developed [150,151]. The first paper represents a review with the aim of introducing a multi-assay wearable biosensor that would provide continuous tracking of a person's sweat metabolites for authentication purposes. This review looks at many of the assays previously mentioned: ALT/LDH, ALT/POx/HRP, and GlDH, and some that were not mentioned: Alanine and glutamate assay with ALT, glutamate oxidase, and HRP; aspartate using the aspartate transaminase enzyme; and a combined version with all three of these new analytes in a single assay. By monitoring these assays, one can produce output data that would be beneficial in the authentication of a person with many cybersecurity applications. The second paper illustrates the use of three enzyme assays in order to encryp<sup>t</sup> a short message using a basic cipher [151]. The three enzymatic assays used involved HRP, lysozyme, and ALP. HRP and ALP were used as previously mentioned. Lysozyme breaks down cell walls from cells added during the assay to produce a reduction in signal at 450 nm, acting as the recognition element. The data resulting from the colorimetric assays are used in the encryption of a message. Provided that the receiver of the message performs the same experiment under the same conditions, the message will be properly decrypted. The data from these enzymatic assays act as "keys" that one use in order to lock and unlock data in relation to encryption.

This brief combination of cryptology and biosensors can have a large impact on the future of user authentication, cryptography, and unconventional computing as a whole. The processes outlined here can be combined with biometrics for user authentication, which is considered just as, or more, important compared to data security through encryption. In cryptography, the further research of other biosensor systems combined with stronger and more robust encryption methods can lead to the advancement of these systems to be used instead of random number generators, which have been controversial for use in cryptography since their inception [152]. Going even further, biosensors can be further researched for direct encryption of data to provide an alternative to the widely researched encryption via DNA [94–102,122–126,153–157].

## **3. Conclusions**

Current research in biosensors has led to advancement in the use of biosensors on three fronts: Forensics, biometrics, and cybersecurity. In the field of forensics, the use of fingerprint material has been demonstrated to be capable of being used to determine the biological sex of a person through multiple methods. These methods relied on the detection of certain amino acids, some methods consisted of a broad detection of 23 amino acids, and some methods were much more selective and targeted down to a single amino acid. Additionally, the use of another medium, blood, allows one to deterministically estimate the amount of time that the blood has been outside the body for up to 2 days by analyzing the degradation of enzymes present in blood. Additionally, it was found that a single assay was able to not only estimate this time since deposition, but to also estimate the age of the originator. Sweat has been the third major medium in forensic endeavors, building upon the fingerprint analysis as fingerprints contain sweat. A novel methodology for a lactate-detecting on-site testing strip was developed in order to identify the presence of sweat due to the high concentration of lactate in sweat. This method was highly sensitive and required extremely small volumes of sweat to produce a tangible response. Sweat has also been examined for other purposes, showing that one can detect the presence of ethanol in sweat, providing another method of determining intoxication levels besides a breathalyzer or invasive blood techniques, in addition to detecting other drugs of abuse. Sweat was further analyzed for biometric purposes by comparing the levels of three metabolites found in sweat to differentiate individuals. Lastly, methods involving biosensors for both the authentication of individuals and for cryptography were developed, benefitting two major establishments of cybersecurity.

In the future, biosensors can further fulfill the expansion of these three fields with additional research. In the field of forensics, a wider array of metabolites may be examined for use in a device that would analyze a certain body fluid and provide more information relating to the habits and identifying information of the originator in addition to the biological sex and age mentioned previously. Additionally, more research can be performed in order to provide for a broad testing kit with higher accuracy and precision for various compounds, illicit and legal, for use in roadside testing to aid law enforcement o fficers. Biometrics and biosensors are closely related, as shown by the research seen here. Further analysis utilizing monitoring and other metabolite tracking will reinforce not only the strengths in the use of this methodology but also possibly reduce or remove the current unknowns and limitations for this method. Lastly, the use of di fferent bioa ffinity-based assay systems for cryptography for the use of di fferent cipher systems will provide a reliable alternative to the random number generator systems used in cryptography today. This work in cybersecurity can also be combined with biometrics for user authentication for digital and evolving systems. Biosensors have been an important facet in the fields of clinical diagnostics, environmental processes, and military devices, and is a strong emerging technique in the fields of forensic science, biometrics, and cybersecurity. In these three fields, biosensors have produced considerable results thus far and have an auspicious future for further research.

**Funding:** This research was funded by NIJ gran<sup>t</sup> number 2016-DN-BX-0188.

**Conflicts of Interest:** The authors declare no conflict of interest.
