Terahertz Technology Advances Microbiology, Enabling Quantitative Microbial Measurement and Manipulation over Two Decades

Microorganisms play a critical role in all life, and advances in detecting and understanding them have broad implications for medicine, environmental science, and industry. Ding Cao, Guangyou Fang, and Xuequan Chen, from the GBA Branch of Aerospace Information Research Institute, Chinese Academy of Sciences, have contributed to a growing body of work exploring the potential of terahertz technology in microbiology. Their review highlights how terahertz waves, uniquely sensitive to water and molecular motion, offer a non-invasive and label-free method for both studying microbial function and accurately identifying different types of microorganisms. This research represents a significant step towards bridging the gap between terahertz photonics and microbiology, paving the way for new tools and deeper insights into the microbial world.

Terahertz Sensing for Pathogen Detection and Analysis

Research into terahertz (THz) sensing and imaging is rapidly advancing, with a strong focus on biomedical applications, particularly detecting pathogens and analysing bacteria. This work explores how THz radiation interacts with microorganisms, offering new ways to identify and understand these biological systems. Researchers are successfully detecting viral proteins and identifying bacterial colonies using this technology, and are extending this analysis to detect biomarkers beyond pathogens, including neurotransmitters and DNA. Detailed analysis extends to assessing bacterial viability, identifying species, and differentiating between bacterial domains within biofilms.

THz imaging allows researchers to analyse the refractive properties of living cells without damaging them, and high-resolution techniques are pushing the limits of resolution using innovative approaches like near-field imaging and solid immersion lenses. Automation and increased throughput are being achieved by integrating THz sensors with microfluidic devices. Central to these advancements are engineered materials called metamaterials and metasurfaces, which enhance sensitivity and specificity by boosting absorption, controlling resonant frequencies, amplifying signals, and manipulating polarization. Current research focuses on improving the sensitivity of THz sensors to detect low concentrations of target molecules and developing sensors that require no labels, avoiding the need for fluorescent or radioactive markers. Emerging trends include integrating THz data analysis with artificial intelligence and machine learning to improve detection accuracy and classification. Researchers are also developing portable and affordable THz sensors for point-of-care diagnostics and real-time monitoring of biological processes, demonstrating the significant potential of terahertz sensing and imaging for a wide range of biomedical applications.

Terahertz Radiation Confirms Absence of Genetic Damage

Researchers are pioneering the use of terahertz (THz) radiation to investigate and manipulate microorganisms, building on its unique properties, including sensitivity to water and molecular motions, non-invasive nature, and low photon energy. Rigorous safety assessments, exposing five bacterial strains to 1. 6THz pulsed laser radiation, ultraviolet radiation, and chemical stimulants, consistently demonstrated that THz radiation did not induce mutagenic properties or inflict DNA damage, unlike UV radiation and chemical stimulants. This work confirms that the photon energy of THz waves is insufficient to break molecular bonds and cause genetic mutations.

Beyond assessing safety, researchers investigated the biological effects of THz radiation on various microorganisms, revealing an increased growth rate in yeast cells specifically at 341GHz, and alterations in protein expression levels in Archaea. Notably, submillimeter-wave radiation promoted the separation of frustules from diatom algae cell membranes. To harness microbial responses, scientists engineered E. coli as THz-sensitive biosensors by linking genes sensitive to heavy metals with genes expressing fluorescence within a plasmid. By observing bacterial fluorescence, researchers can detect the presence of heavy metals, and this approach has been refined since 2013 using plasmids containing a promoter and a reporter gene, such as green fluorescent protein (GFP). For example, the katG gene promoter, encoding for hydroperoxidase I, was used with a pKatG-GFP plasmid, demonstrating increased GFP expression under THz radiation, and providing a means to study hydrogen peroxide-degrading metabolic pathways. Similar increasing gene expressions were observed using promoters of other sensor genes, including copA, emrR, matA, safA, chbB, and tdcR, demonstrating the potential for THz radiation to serve as a stimulus for studying microbial metabolism and developing novel biosensing technologies.

Terahertz Radiation Alters Bacterial Gene Expression

Terahertz (THz) radiation is emerging as a powerful tool for microbiology, demonstrating unique non-thermal effects on microorganisms. Studies reveal that exposing E. coli to a continuous wave of 3. 1THz resulted in an increase in plasmid copy number and red fluorescence protein production. Investigations into transcriptional activity demonstrate significant impacts on processes including abortive initiation and pausing under THz radiation, and analysis of a broadband synchrotron source of 0.

5-18THz revealed cellular responses related to osmotic stress, plasma membrane regulation, and phospholipid biosynthesis. Researchers also examined the extremophilic bacterium Geobacillus icigianus, observing changes in metabolic pathways such as chemotaxis and the synthesis of peptidoglycan and riboflavin following both short-term and long-term THz exposures, primarily attributed to disturbances in the expression of genes related to copper, iron, and zinc homeostasis. Importantly, studies consistently demonstrate that THz radiation, unlike UV radiation or chemical stimulants, does not cause genetic mutations or DNA damage in bacterial cells, as confirmed by Ames tests on five different bacterial strains. Beyond bacteria, investigations on yeast cells showed an increased growth rate specifically at 341GHz, while studies on Archaea revealed alterations in the expression levels of 16 proteins upon THz exposure.

Notably, submillimeter-wave radiation promoted the separation of frustules from diatom algae cell membranes. Scientists are now leveraging these biological effects to create THz-sensitive biosensors, utilizing genetically engineered E. coli to detect metabolic pathways. Transforming E. coli with a plasmid containing the katG gene promoter linked to green fluorescent protein (GFP) resulted in increased GFP expression under THZ radiation, indicating higher expression of hydroperoxidase I and providing a means to study hydrogen peroxide-degrading metabolic pathways. Similar increasing gene expressions were observed using promoters of other sensor genes, including copA, emrR, matA, safA.