Identification and quantitative detection of two pathogenic bacteria based on a terahertz metasensor

Broad-spectrum pathogenic bacteria SERS sensing with face-centered high-index facets Au CPNCs & microarray chips: A novel platform able to achieve dual-readout detection

Non-specificity and inadequate quantitative capability are the primary challenges faced by the surface-enhanced Raman scattering (SERS) technique, especially when it comes to detecting bacteria in real samples. Herein, a novel face-centered Au Convex Polyhedral Nanocrystal (Au CPNC) with high-index facets and its assembly Au CPNCs microarray chip were designed and fabricated to address these challenges, within the process where 4-mercaptophenylboronic acid (4-MPBA) was utilized as a multifunctional element. The as-prepared Au CPNC possesses anisotropic raised edges enjoying tunable localized surface plasmon resonance modes for SERS enhancement. Then we obtained long-region ordered Au CPNCs microarrays equipping even greater "hot spots" with a SERS enhancement factor (EF) up to 5.38 × 107. The constructed SERS probes excellently leveraged the outstanding SERS performance of Au CPNC and the superior functions of 4-MPBA, which enabled the differences among the bacterial "fingerprints" to be highlighted. Through partial least squares discriminant analysis (PLS-DA), we successfully identified Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Listeria monocytogenes with achieving limits of detection (LODs) in spiked whole blood samples of 3, 1, 2, and 2 cfu/mL, respectively. Notably, the LODs for all samples by SERS mapping visual readout mode were as low as 10 cfu/mL. In practical applications, our method demonstrated its efficacy by 100 % accurately classifying (20 cases) of real blood samples. Altogether, the theoretical significance and application value of this study reside in providing fundamental insights and approaches for the development of pathogenic bacteria detection field.

Terahertz molecular vibrational sensing using 3D printed anapole meta-biosensor

Terahertz (THz) fingerprint sensing utilizes the absorption of fingerprints generated by the unique vibrational characteristics of molecules to achieve substance-specific identification. By taking full advance of the anapole mode induced-biosensor consisting of out-of-plane metal-insulator-metal (MIM) configuration, the D-glucose solutions down to physiological level are accurately detected by proposed metasurface biosensor through the electromagnetic induced absorption (EIA) effect induced by the interaction between the metasurface and molecular vibrational fingerprint. Besides, by utilizing the vibrational fingerprint sensing ability, the pure D-glutamic acid and D-lactose, as well as their mixture have been quantitatively characterized. In addition, with the aid of machine learning algorithms, the designed single resonance metasensor achieves 100% recognition of five molecules. This work brings a convincing strategy for trace label-free molecular recognition for various species, which might extend the promising potentials of THz sensing techniques toward biomedical testing and clinical diagnosis.

Advances in in vitro cultivation techniques for comprehensive analysis of human gut microbiome

The role of gut microbiota in human health and disease is becoming increasingly recognized. Historically, the impact of human gut microbiota on health has been studied using clinical trials and animal models. However, clinical studies often struggle with controlling variables and pinpointing disease-causing factors, while animal models fall short of accurately replicating the human gut environment. Additionally, continuous sample collection for gut microbiota analysis in vivo presents significant ethical and technical challenges. To address these limitations, in vitro fermentation models have emerged as promising alternatives. These models aim to simulate the structural and functional characteristics of the human gut in a controlled setting, offering valuable insights into microbial behavior. This review highlights current knowledge and technological advances in in vitro cultivation systems for human gut microbiota, focusing on key elements such as three-dimensional scaffolds, culture media, fermentation systems, and analytical techniques. By examining these components, the review establishes a framework for improving methods to cultivate and study human gut microbiota, enhancing research methodologies for better understanding microbial interactions, behavior, and adaptation in diverse environments.

Single-Bacterium Diagnosis via Terahertz Near-Field Dielectric Nanoimaging

Single-bacterium diagnostic methods with unprecedented precision and rapid turnaround times are promising tools for facilitating the transition from empirical treatment to personalized anti-infection treatment. Terahertz (THz) radiation, a cutting-edge technology for identifying pathogens, enables the label-free and non-destructive detection of intermolecular vibrational modes and bacterial dielectric properties. However, this individual dielectric property-based detection and the mismatched spatial resolution are limited for the single-bacterium identification of various species of pathogens. Here, we demonstrate a single-bacterium THz dielectric nanoimaging (STDN) strategy by customized THz scattering-type scanning near-field optical microscopy. The THz nanoimages of bacteria are explained and confirmed by theoretical modeling and near-field measurement. By synchronously tracking the bacterial intrinsic dielectric property and extrinsic morphology, the strategy achieved 99.3% and 91.6% accuracy in species identification and antibiotic susceptibility testing with the trained classifier within 2 hours. This proof-of-concept STDN strategy may propel precise bacterial infection management and help to counteract antibiotic resistance.

The theory, technology, and application of terahertz metamaterial biosensors: A review

Terahertz metamaterial biosensors combine terahertz time-domain spectroscopy with metamaterial sensing to provide a sensitive detection platform for a variety of targets, including biological molecules, proteins, cells, and viruses. These biosensors are characterized by their rapid response, sensitivity, non-destructive, label-free operation, minimal sample requirement, and user-friendly design, which also allows for integration with various technical approaches. Advancing beyond traditional biosensors, terahertz metamaterial biosensors facilitate rapid and non-destructive trace detection in biomedical applications, contributing to timely diagnosis and early screening of diseases. In this paper, the theoretical basis and advanced progress of these biosensors are discussed in depth, focusing on three key areas: improving the sensitivity and specificity, and reducing the influence of water absorption in biological samples. This paper also analyzes the potential and future development of these biosensors for expanded applications. It highlights their potential for multi-band tuning, intelligent operations, and flexible, wearable biosensor applications. This review provides a valuable reference for the follow-up research and application of terahertz metamaterial biosensors in the field of biomedical detection.

Rapid, ultrasensitive, and specific RPA-THz system for pathogenic microorganism detection

Pathogenic microorganisms responsible for infectious diseases pose a significant global threat to human health. Existing detection methods, such as qPCR and ELISA, fail to simultaneously meet the requirements for high sensitivity, high specificity, and rapid detection. This study presents an innovative approach for the rapid, specific, and highly sensitive detection of pathogenic microorganisms, particularly Escherichia coli O157:H7 (E. coli O157:H7) and varicella-zoster virus (VZV), by combining recombinase polymerase amplification (RPA) with terahertz time-domain spectroscopy (THz-TDS). The qualitative and quantitative detection method for pathogenic microorganisms was developed and evaluated. The stable and efficient RPA reaction systems were established to specifically amplify the key conserved genes of these pathogens. Then the RPA products were purified, and enriched with MBs. The absorbance spectra were obtained using THz-TDS technology. The linear range of the RPA-THz for detecting E. coli O157:H7 was 0.55 to 5.5 × 104 pg/mL, while for VZV, it was 0.75 to 7.5 × 103 pg/mL. The limit of detection (LOD) for bacteria and viruses was 0.226 pg/mL and 0.528 pg/mL, respectively, demonstrating better sensitivity than the qPCR (550 pg/mL and 750 pg/mL, respectively). In addition, the whole amplification and detection process was completed in about 35 minutes. Compared to traditional pathogen detection techniques, the primary advantage of the developed RPA-THz method exhibited high accuracy, good reproducibility, and short detection times, enabling non-ionizing, label-free analysis for rapid detection with high sensitivity and specificity of pathogenic microorganisms. This study provides a theoretical foundation and practical demonstration for the fast and precise detection of pathogenic microorganisms. It establishes a crucial research basis for further development of RPA-THz sensors, advancing technological progress in the field of food safety, medical diagnostics, environmental monitoring, and public health.

Ultrasensitive Terahertz Label-Free Metasensors Enabled by Quasi-Bound States in the Continuum

Advanced sensing devices based on metasurfaces have emerged as a revolutionary platform for innovative label-free biosensors, holding promise for early diagnostics and the detection of low-concentration analytes. Here, we developed a chip-based ultrasensitive terahertz (THz) metasensor, leveraging a quasi-bound state in the continuum (q-BIC) to address the challenges associated with intricate operations in trace biochemical detection. The metasensor design features an open-ring resonator metasurface, which supports magnetic dipole q-BIC combining functionalized gold nanoparticles (AuNPs) bound with a specific antibody. The substantial enhancement in THz-analyte interactions, facilitated by the potent near-field enhancement enabled by the q-BICs, results in a substantial boost in biosensor sensitivity by up to 560 GHz/refractive index units. This methodology allows for the detection of conjugated antibody-AuNPs for cardiac troponin I at concentrations as low as 0.5 pg/ml. These discoveries deliver valuable insight for AuNP-based trace biomolecule sensing and pave the path for the development of chip-scale biosensors with profound light-matter interactions.

Characteristic fingerprint spectrum of α-synuclein mutants on terahertz time-domain spectroscopy

α-Synuclein, a presynaptic neuronal protein encoded by the SNCA gene, is involved in the pathogenesis of Parkinson's disease. Point mutations and multiplications of α-synuclein (A30P and A53T) are correlated with early-onset Parkinson's disease characterized by rapid progression and poor prognosis. Currently, the clinical identification of SNCA variants, especially disease-related A30P and A53T mutants, remains challenging and also time consuming. This study aimed to develop a novel label-free detection method for distinguishing the SNCA mutants using transmission terahertz (THz) time-domain spectroscopy. The protein was spin-coated onto the quartz to form a thin film, which was measured using THz time-domain spectroscopy. The spectral characteristics of THz broadband pulse waves of α-synuclein protein variants (SNCA wild type, A30P, and A53T) at different frequencies were analyzed via Fourier transform. The amplitude A intensity (AWT, AA30P, and AA53T) and peak occurrence time in THz time-domain spectroscopy sensitively distinguished the three protein variants. The phase φ difference in THz frequency domain followed the trend of φWT > φA30P > φA53T. There was a significant difference in THz frequency amplitude A' corresponding to the frequency ranging from 0.4 to 0.66 THz (A'A53T > A'A30P > A'WT). At a frequency of 0.4-0.6 THz, the transmission T of THz waves distinguished three variants (TA53T > TA30P > TWT), whereas there was no difference in the transmission T at 0.66 THz. The SNCA wild-type protein and two mutant variants (A30P and A53T) had distinct characteristic fingerprint spectra on THz time-domain spectroscopy. This novel label-free detection method has great potential for the differential diagnosis of Parkinson's disease subtypes.

Enhancement of wide-band trace terahertz absorption spectroscopy based on microstructures: a review

Research on the interaction between nanoscale materials and light holds significant scientific significance for the development of fields such as optoelectronic conversion and biosensing. The study of micro- and nano-optics has produced numerous outstanding research achievements by utilizing the dielectric optical coupling mechanism and plasmon effects to enhance the interaction between light and matter. These findings have demonstrated tremendous potential for applications in the field of molecular fingerprint sensing. This review focuses on a retrospective analysis of recent research studies in the enhancement of wide-band trace terahertz absorption spectroscopy. The physical mechanisms of using waveguide structures, dielectric metasurfaces/meta-gratings, and spoof surface plasmon polaritons (SSPs) to improve the interaction between light and trace-amount matters are introduced. The new approaches and methods for enhancing broad-band terahertz absorption spectroscopy of trace samples using microstructure designs are discussed. Additionally, we elucidate the scientific ideas and exploratory achievements in enhancing terahertz fingerprint spectroscopy detection. Finally, we provide an outlook on the research and development direction and potential practical applications of absorption spectroscopy enhancement detection.