High-sensitivity Measurements Research Articles

Development and verification of crossing priming amplification on rapid detection of virulent and viable L. monocytogenes: In-depth analysis on the target and further application on food screening

Virulent Listeria monocytogenes is responsible for listeriosis, a highly fatal foodborne illness that impairs human health. One of the major causes of its pathogenicity is the carriage of virulence factor, listeriolysin O, encoded by hylA gene. Herein, the specificity and conservativity of hylA gene sequences were analyzed, with most conservative region selected. Then, a crossing priming amplification (CPA) assay targeting hylA conservative region was established under an isothermal condition (63 °C) to identify virulent L. monocytogenes within 60 min. Forty-four reference strains including two standard L. monocytogenes strains and forty-two strains of other species were selected to assess sensitivity and specificity. The CPA assay showed strong specificity and sensitivity (genomic DNA at 5.66 pg/μL). The practicality of the CPA assay was further confirmed in four artificially contaminated rice-flour products with limit of detection at 104 CFU/mL. In addition, a PMA-CPA assay was developed to direct detect L. monocytogenes viable cells with rice-flour products as a model system. In conclusion, the developed CPA method has advantages of high sensitivity, specificity and quick measurement in the detection of virulent L. monocytogenes, showing considerably feasible promise for future food safety.

Femtosecond laser etching C-type fiber optic vernier sensor for seawater temperature and salinity measurements

In this work, we demonstrate a dual C-type fiber optic vernier sensor based on femtosecond laser etching for measuring seawater temperature and salinity. The C-type fibers are etched using femtosecond laser microfabrication technology on hollow-core fibers (HCF), including temperature and salinity cavities. The seawater can fully flow into the salinity cavity as a sensing medium, and the polydimethylsiloxane (PDMS) is filled into the temperature cavity as a sensitizing medium. Combined with the vernier effect, dual parameter high sensitivity simultaneous measurement is achieved. Through simulation and experimental testing, the sensor can achieve high sensitivity measurement of seawater salinity and temperature, with sensitivities of −2.69 nm/‰ and −4.54 nm/℃, respectively. In the stability tests of salinity and temperature, the maximum interference wavelength shifts are 0.52 nm and 0.64 nm, respectively. In the repeated measurement experiment, the maximum deviation of sensitivity for salinity cavity and temperature cavity measurements are 0.03 nm/‰ and 0.18 nm/℃, respectively, indicating that the structure has good measurement stability and repeatability. This sensor has the advantages of strong stability, good repeatability, and low cost, which can be used as a new type of sensor to achieve high-sensitivity detection of seawater parameters.

Proposal for a New Differential High-Sensitivity Refractometer for the Simultaneous Measurement of Two Refractive Indices and Their Differences.

The refractive index of a liquid serves as a fundamental parameter reflecting its composition, thereby enabling the determination of component concentrations in various fields such as chemical research, the food industry, and environmental monitoring. Traditional methods for refractive index (RI) measurement rely on light deflection angles at interfaces between the liquid and a material with a known refractive index. In this paper, the authors present a new differential refractometer for the highly sensitive measurement of RI differences between two liquid samples. Using a configuration with two cells equipped with flat parallel plates as measuring elements, the instrument facilitates accurate analysis. Namely, the sensor signals from both the solution and the solvent cuvette are generated simultaneously with one laser pulse, reducing the possible fluctuations in the laser radiation intensity. Our evaluation shows the high sensitivity of RI measurements <7×10-6), so this differential refractometer can be proposed not only as a high-sensitivity sensing tool that can be used for mobile detection of nanoparticles in solution samples but also to determine the level of environmental nano-pollution using water (including rain, snow) samples from various natural as well as industrial sources, thus helping to solve some important environmental problems.

A Differential and High-Sensitivity Thickness Measurement Sensor for Dielectric Solid Materials Using a Branch Line Coupler

A Differential and High-Sensitivity Thickness Measurement Sensor for Dielectric Solid Materials Using a Branch Line Coupler

Bulk lysis procedures alter target cell population counts.

To achieve high-sensitivity cell measurements (<1 in 105 cells) by flow cytometry (FCM), the minimum number of acquired cells must be considered and conventional immunophenotyping protocols fall short of these numbers. The bulk lysis (BL) assay is a standardized erythrocyte lysing approach that allows the analysis of the millions of cells required for high-sensitivity measurable residual disease (MRD) detection. However, this approach has been associated with significant cell loss, along with potential over or underestimates of rare cells when using this method. The aim of this study was to evaluate bulk lysis protocols and compare them with minimal sample perturbation (MSP) protocols, which are reported to better preserve the native cellular state and avoid significant cell loss due to washing steps. To achieve this purpose, we first generated an MRD model by spiking fresh peripheral blood with K562 cells, stably expressing EGFP, at known percentages of EGFP positive cells to leukocytes. Samples were then prepared with BL and MSP protocols and analyzed using FCM. For all percentages of K562 cells established and evaluated, a significant decrease of this population was detected in BL samples compared with MSP samples, even at low K562 cell percentages. Significant decreases for non-necrotic cells were also observed in BL samples relative to MSP samples. In conclusion, the evaluation of the potential effects of BL protocols in obtaining the final count is of great interest, especially for over- or under-estimation of target cells, as in the case of measurable residual disease. Since conventional flow cytometry or minimal sample perturbation assays fall short in obtaining the minimum numbers required to reach high sensitivity measurements, significant efforts may be needed to improve bulk lysis solution reagents.

High-sensitivity strain sensor based on an asymmetric tapered air microbubble Fabry-Pérot interferometer with an ultrathin wall

A Fabry-Pérot interferometer (FPI) with an asymmetric tapered structure and air microbubble with an ultrathin wall is designed for high-sensitivity strain measurement. The sensor contains an air microbubble formed by two single-mode fibers (SMF) prepared by fusion splicer arc discharge, and a taper is applied to one side of the air microbubble with a wall thickness of 3.6 µm. In this unique asymmetric structure, the microbubble is more easily deformed under stress, and the strain sensitivity of the sensor is up to 15.89 pm/µɛ as evidenced by experiments.The temperature sensitivity and cross-sensitivity of the sensor are 1.09 pm/°C and 0.069 µɛ/°C in the temperature range of 25-200°C, respectively, thus reducing the measurement error arising from temperature variations. The sensor has notable virtues such as high strain sensitivity, low-temperature sensitivity, low-temperature cross-sensitivity, simple and safe process preparation, and low cost. Experiments confirm that the sensor has good stability and repeatability, and it has high commercial potential, especially strain measurements in complex environments.

Ammonia-trapping multilayer polymer urease film amplifier coated surface plasmon resonance sensor for ultra-sensitive urea detection

In this paper, we have developed a new urea signal amplification technology based on a multilayer urease polymer film self-assembly structure for the first time, enabling the realization of ultra-accurate urea optical detection. We demonstrate the effectiveness of this technique based on surface plasmon resonance (SPR) platform. When the urea signal amplifier is combined with SPR sensors, multilayer urease polymer film contacts with urea molecules, the urea molecules are oxidated into NH3 and CO2, causing the pH increase, which weakens the electrostatic interaction between different polymer layers and induces the RI reduction of the multilayer urease film, thereby causing the shift of the SPR spectrum. Experiment results confirm that urea sensitivity has been improved 12-fold, and the limit of detection (LOD) has been optimized to less than 10−3 mmol/L. Furthermore, the anti-interference has been improved 22.8-fold and is kept even the interference signal strength increases by 100 times. Moreover, multilayered urease polymer leads to the increase of urease on the sensor surface, thus expanding the detection range of urea by 3.5 times. This provides a new way to solve the contradiction between high sensitivity and large measurement range of optical fiber biosensor. Importantly, the concept of using enzyme-loaded polymer films for signal amplification can be adapted for the detection of various other biomolecules by replacing the enzyme with a specific recognition element for the target molecule. This opens doors for developing highly sensitive and specific biosensors for diverse applications in healthcare, environmental monitoring, and food safety.

Optical Fiber Surface Plasmon Resonance Sensor for Glyceryl Tributyrate Detection Based on the PAA/CS Composite Hydrogel Embedding Protease Method.

Glycerol tributyrate as a low-density lipoprotein plays a crucial role in drug development and food safety. In this work, a novel high-stability fiber optic sensor for glyceryl tributyrate based on the poly(acrylic acid) (PAA) and chitosan (CS) composite hydrogel embedding method is first proposed. Compared with traditional functionalization, the lipase in a polymer network structure used in this article can not only avoid chemical reactions that cause damage to the enzyme structure but also avoid the instability of ionic bonds and physical adsorption. Therefore, the PAA/CS hydrogel method proposed in this article can effectively retain enzyme structure. First, the impact of different layers (one to five layers) of PAA/CS on pH sensing performance was explored, and it was determined that layers 1-3 could be used for subsequent sensing experiments. Within the linear detection range of 0.5-10 mM, the detection sensitivities of the one to three layers of the biosensor are divided into 0.65, 0.95, and 1.51 nm/mM, respectively, with the three layers having the best effect. When the number of coating layers is three, the detection limit of the sensor is 0.47 mM, meeting the millimole level detection standard for anticancer requirement. Furthermore, the stability and selectivity of the sensor (in the presence of hemoglobin, urea, cholesterol, acetylcholine, and glucose) were analyzed. The three-layer sensor is used for sample detection. At concentrations of 1-10 mM, the absolute value of the recovery percentage (%) is 82-99%, which can accurately detect samples. The sensor proposed in this paper has the advantages of low sample consumption, high sensitivity, simple structure, and label-free measurement. The enzyme-embedding method provides a new route for rapid and reliable glyceryl tributyrate detection, which has potential applications in food safety as well as the development of anticancer drugs.

Label-free SPR fiber microfluidic sensor with PDA-MA cross-linked lipase for specific detection of tributyrin

As a precursor to butyric acid and also a short-chain triglyceride, tributyrin plays an important role in repairing small intestinal villi, promoting the absorption and utilization of nutrients, and monitoring human health. The traditional carboxylation functionalization method of optical fiber sensors takes a long time and is complicated to operate. Therefore, we need a sensor with a functional period, high sensitivity, and the ability to quickly detect samples to achieve specific detection of tributyrin. In this paper, based on the chemical cross-linking method of polydopamine-maleic acid (PDA-MA), a novel fiber-optic microfluidic surface plasmon resonance (SPR) sensor was proposed to realize the detection of tributyrin. Compared with the traditional functionalization method, the fixation method of PDA-MA chemical cross-linking method not only shortens the functionalization time, but also increases the sensitivity of the sensor. Experimental results show that the sensitivity of the microfluidic sensor coated with PDA reaches 3392.7 nm/RIU, which is 1.75 times that of the uncoated sensor. The sensor has a sensitivity of 8.22 nm/mM in the range of 0.5–5 mM and a response time of only 8 min at the concentration of 1 mM. In addition, the sample detection error of the sensor is within 12 % in the range of 0.5–5 mM. The proposed sensor offers the advantages of low sample consumption (100 μL), high sensitivity, good selectivity, good repeatability, anti-interference ability, and label-free measurement. The sensor holds promising applications in food safety and health monitoring due to its superior performance.

The Implementation of AFM-Based Nanoscale Diagnostic Methods in the Investigation of the Degradation Process of Bacteriostatic Acrylic Film with Silver Nanoparticles

In this paper, a custom-tailored investigation protocol aimed at the tests of the resistance of bacteriostatic acrylic-based film containing silver nanoparticles is presented. As hospital appliance applications were considered, it was necessary to provide a unique approach, enabling specific media exposure and utilizing high-sensitivity measurement methods to observe fine indications of material wear. Due to the presence of nanoparticles in the tested film, nanometer-resolution surface imaging is necessary. Therefore, the main source of information about its degradation process is atomic force microscopy (AFM) measurements. This particular tool is an appreciated source of information, providing quantitative data about both morphological and mechanical changes in the properties of the surface. Using such an approach, supported by standard diagnostic methods, such as colorimetry and wettability angle determination, it was possible to enable insights into the way the bacteriostatic film deteriorates and evaluate its usefulness in medical appliance applications. Further tests of various films developed by companies can be performed using the described protocol to determine the lifetime of certain products. This paper reveals the company’s practical utilization of both standardized and novel test techniques in the evaluation of new products.

Experimental study on ultra-high sensitivity gold-based SPR sensor for refractive index and temperature measurement

We have experimentally demonstrated an ultra-high sensitivity gold-based fiber refractive index (RI) sensor whose main structure is composed of multimode fiber (MMF) and photonic crystal fiber (PCF). The gold film is deposited on V-shaped PCF by magnetron sputtering, and sensing experiments are performed based on the principle of surface plasmon resonance (SPR). Numerical simulation results indicate that the cladding mode of the V-shaped PCF is more capable of stimulating the SPR effect than the core mode. The experimental results show that the RI measurement range of the sensor is 1.333–1.421, with a maximum sensitivity of 10015 nm/RIU. In addition to RI sensing, sensing probes can be coated with polydimethylsiloxane (PDMS) on a gold film for temperature sensing. For temperature detection, the range is from 10 to 100 °C and the maximum sensitivity is 3.5 nm/℃. Besides high sensitivity in RI measurement, the proposed sensor also has good sensing performance in temperature sensing. With the advantages of high sensitivity, good stability, and easy preparation, this sensor has become an important reference in the field of high-performance sensing.

Glycerophospholipid polyunsaturation modulates resveratrol action on biomimetic membranes

The phytoalexin resveratrol has received increasing attention for its potential to prevent oxidative damages in human organism. To shed further light on molecular mechanisms of its interaction with lipid membranes we study resveratrol influence on the organisation and mechanical properties of biomimetic lipid systems composed of synthetic phosphatidylcholines with mixed aliphatic chains and different degree of unsaturation at sn-2 position (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, and 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine, PDPC). High-sensitivity isothermal titration calorimetric measurements reveal stronger spontaneous resveratrol association to polyunsaturated phosphatidylcholine bilayers compared to the monounsaturated ones resulting from hydrophobic interactions, conformational changes of the interacting species and desolvation of molecular surfaces. The latter is supported by the results from Laurdan spectroscopy of large unilamellar vesicles providing data on hydration at the glycerol backbones of glycerophospholipides. Higher degree of lipid order is reported for POPC membranes compared to PDPC. While resveratrol mostly enhances the hydration of PDPC membranes, increasing POPC dehydration is reported upon treatment with the polyphenol. Dehydration of the polyunsaturated lipid bilayers is measured only at the highest phytoalexin content studied (resveratrol/lipid 0.5 mol/mol) and is less pronounced than the effect reported for POPC membranes. The polyphenol effect on membrane mechanics is probed by thermal shape fluctuation analysis of quasispherical giant unilamellar vesicles. Markedly different trend of the bending elasticity with increasing resveratrol concentration is reported for the two types of phospholipid bilayers studied. POPC membranes become more rigid in the presence of resveratrol, whereas PDPC-containing bilayers exhibit softening at lower concentrations of the polyphenol followed by a slight growth without bilayer stiffening even at the highest resveratrol content explored. The new data on the structural organization and membrane properties of resveratrol-treated phosphatidylcholine membranes may underpin the development of future liposomal applications of the polyphenol in medicinal chemistry.

Robust high-order petal-mode laser with tunable topological charge pumped by an axicon-based annular beam

In this work, we demonstrate a watt-level laser producing high-order, petal-shaped output modes with tunable topological charge, by using an axicon-based divergent annular pump beam. The topological charge of the output beam could be varied in the range of 34–72 by adjusting the position of the Nd:YVO4 crystal relative to the focal plane of the pump beam. The highest order petal-mode beam generated from the system had a topological charge of 72 and a power of 1.3 W. The highest output power up to 2.1 W with a topological charge of 34 was achieved at an absorbed pump power of 5.8 W. The generated output modes were observed to be robust under power scaling and on propagation, with the same spatial profiles being maintained in the near- and far-fields. We anticipate that this system design may find use as a laser source in applications such as 3D optical trapping, fabrication of optical vortex arrays, optical communications, and high-sensitivity spatial measurement.

ZnOHF-ZnO nanomaterial-coated macro-bend fiber triethylamine gas sensor working at room temperature

This study presents a room temperature triethylamine (TEA) gas sensor based on the macro-bend fiber. The sensor achieves the rapid and high sensitivity measurement of TEA gas by coating the bending section of the optical fiber with ZnOHF-ZnO nanomaterial. The macro-bend fiber structure increases the penetration depth of the evanescent field transmitting along the no-core optical fiber (NCF), what allowing more light to leak into layer of the gas-sensitive material and thus enhancing the sensitivity to TEA gas. Different sensing probes were fabricated and compared for the coating layers with ZnOHF and ZnOHF-ZnO, respectively. The results showed that the sensitivity of the ZnOHF-ZnO coated sensor was 0.0044 dB/ppm, which was three times higher than that of the ZnOHF-coated sensor. Other sensing performance was experimentally demonstrated with a limit of detection (LOD) of 1 ppm, a response time of 16 s, and a recovery time of 18 s, enabling fast detection for TEA gas. Finally, the working mechanism has been explained. This macro-bend fiber-based TEA gas sensor has the advantages of small size, low operating temperature, fast response time, and good selectivity, making it suitable for the rapid identification and detection of TEA gas.

Sensitivity volume as figure-of-merit for maximizing data importance in electrical impedance tomography

Objective. Electrical impedance tomography (EIT) is a noninvasive imaging method whereby electrical measurements on the periphery of a heterogeneous conductor are inverted to map its internal conductivity. The EIT method proposed here aims to improve computational speed and noise tolerance by introducing sensitivity volume as a figure-of-merit for comparing EIT measurement protocols. Approach. Each measurement is shown to correspond to a sensitivity vector in model space, such that the set of measurements, in turn, corresponds to a set of vectors that subtend a sensitivity volume in model space. A maximal sensitivity volume identifies the measurement protocol with the greatest sensitivity and greatest mutual orthogonality. A distinguishability criterion is generalized to quantify the increased noise tolerance of high sensitivity measurements. Main result. The sensitivity volume method allows the model space dimension to be minimized to match that of the data space, and the data importance to be increased within an expanded space of measurements defined by an increased number of contacts. Significance. The reduction in model space dimension is shown to increase computational efficiency, accelerating tomographic inversion by several orders of magnitude, while the enhanced sensitivity tolerates higher noise levels up to several orders of magnitude larger than standard methods.

Quantitative, high-sensitivity measurement of liquid analytes using a smartphone compass

Smartphone ubiquity has led to rapid developments in portable diagnostics. While successful, such platforms are predominantly optics-based, using the smartphone camera as the sensing interface. By contrast, magnetics-based modalities exploiting the smartphone compass (magnetometer) remain unexplored, despite inherent advantages in optically opaque, scattering or auto-fluorescing samples. Here we report smartphone analyte sensing utilizing the built-in magnetometer for signal transduction via analyte-responsive magnetic-hydrogel composites. As these hydrogels dilate in response to targeted stimuli, they displace attached magnetic material relative to the phone’s magnetometer. Using a bilayer hydrogel geometry to amplify this motion allows for sensitive, optics-free, quantitative liquid-based analyte measurements that require neither any electronics nor power beyond that contained within the smartphone itself. We demonstrate this concept with glucose-specific and pH-responsive hydrogels, including glucose detection down to single-digit micromolar concentrations with potential for extension to nanomolar sensitivities. The platform is adaptable to numerous measurands, opening a path towards portable, inexpensive sensing of multiple analytes or biomarkers of interest.

High enrichment and sensitive measurement of oxytetracycline in tea drinks by thermosensitive magnetic molecular imprinting based magnetic solid phase extraction coupled with boron doped carbon dots

As a typical kind of new pollutants, there are still some challenges in the rapid detection of antibiotics. In this work, a sensitive fluorescent probe based on boron-doped carbon dots (B-CDs) in combination with thermo-responsive magnetic molecularly imprinted polymers (T-MMIPs) was constructed for the detection of oxytetracycline (OTC) in tea drinks. T-MMIPs were designed, fabricated and employed to enrich OTC at trace level from tea drinks, and B-CDs were utilized as the fluorescent probe to detect the concentration of OTC. The proposed method exhibited good linear relationship with OTC concentration from 0.2 to 60 μg L−1 and the limit of detection was 0.1 μg L−1. The established method has been successfully validated with tea beverages. Present work was the first attempt application of T-MMIPs in combination with CDs in detection of OTC, and demonstrated that the proposed method endowed the detection of OTC with high selectivity, sensitivity, reliability and wide application prospect, meanwhile offered a new strategy for the method establishment of rapid and sensitive detection of trace antibiotics in food and other matrices.

A novel capacitive sensor featuring surface microstructure and hydrogels for measuring full pressure with high-sensitivity

Compared with positive pressure measurement, which is widely used in many fields, negative pressure measurement is often ignored. However, realizing full pressure measurement, that is, positive and negative pressure measurement, with high sensitivity and wide measurement range, is one of the most urgent development directions and key challenges faced by flexible pressure sensors. To overcome this challenging problem, a highly sensitive full-pressure capacitive sensor with surface microstructure and hydrogels is introduced in this paper. The sensing mechanism of the sensor is implemented by detecting the capacitance change caused by the change in the contact area between the hydrogel and the electrode due to the internal and external pressure difference. The PVA/KOH basic gel material is used to resist shear deformation, and the uniform microstructure on the gel surface is achieved by the template method. How to maximize the sensitivity of positive and negative pressure measurements is discussed by carefully evaluating the design parameters of the sensor. The fabricated sensor has a wide measurement range (-100–250 kPa) with high sensitivity (S = 15.6 nF/kPa) in the negative pressure region and (S = 5.2 nF/kPa) in the positive pressure region. In addition, the sensor exhibits fast response, cycle stability, and low measurement limit, which further enhances its performance advantages. In order to validate the application potential of the sensor, the paper conducts experimental verification using the relationship between wind pressure measurement results and the angle of contact with the sensor, as well as the relationship between vehicle speed and wind pressure magnitude. The results show that the designed sensor has potential application prospects in full pressure measurement.

Functionalized sampling swabs array-based portable ATP bioluminescence sensor with on-site enrichment and high specificity for live Salmonella detection

Live food-borne pathogens, featured with rapid proliferative capacity and high pathogenicity, pose an emerging food safety and public health crisis. The high-sensitivity detection of pathogens is particularly imperative yet remains challenging. This work developed a functionalized nylon swab array with enhanced affinity for Salmonella typhimurium (S.T.) for high-specificity ATP bioluminescence-based S.T. detection. In brief, the nylon swabs (NyS) were turned to N-methylation nylon (NyS-OH) by reacting with formaldehyde, and NyS-OH were further converted to NyS-CA by reacting with carboxylic groups of citric acid (CA) and EDC/NHS solution, for altering the NyS surface energy to favor biomodification. The antibody-immobilized nylon swab (MNyS-Ab) was ready for S.T.-specific adsorption. Three prepared MNyS-Ab were installed on a stirrer to form an MNyS-Ab array, allowing for on-site enrichment of S.T. through absorptive extraction. The enriched S.T. was quantified by measuring the bioluminescence of ATP released from cell lysis utilizing a portable ATP bioluminescence sensor. The bioassay demonstrated a detectable range of 102–107 CFU mL−1 with a detection limit (LOD) of 8 CFU/mL within 35 min. The signal of single MNyS-Ab swabs was 500 times stronger than the direct detection of 106 CFU/mL S.T. The MNyS-Ab array exhibited a 100-fold increase in extraction level compared to a single MNyS. This combination of a portable bioluminescent sensor and modified nylon swab array offers a novel strategy for point-of-care testing of live S.T. strains. It holds promise for high-sensitivity measurements of other pathogens and viruses.

Mouthguard-Type Wearable Sensor for Monitoring Salivary Turbidity to Assess Oral Hygiene.

Salivary turbidity is a promising indicator for evaluating oral hygiene. This study proposed a wearable mouthguard-type sensor for continuous and unconstrained measurement of salivary turbidity. The sensor evaluated turbidity by measuring the light transmittance of saliva with an LED and a phototransistor sealed inside a double-layered mouthguard. The sensor was also embedded with a Bluetooth wireless module, enabling the wireless measurement of turbidity. The mouthguard materials (polyethylene terephthalate-glycol and ethylene-vinyl acetate) and the wavelength of the LED (405 nm) were experimentally determined to achieve high sensitivity in salivary turbidity measurement. The turbidity quantification characteristic of the proposed sensor was evaluated using a turbidity standard solution, and the sensor was capable of turbidity quantification over a wide dynamic range of 1-4000 FTU (formazine turbidity unit), including reported salivary turbidity (400-800 FTU). In vitro turbidity measurement using a saliva sample showed 553 FTU, which is equivalent to the same sample measured with a spectrophotometer (576 FTU). Moreover, in vivo experiments also showed results equivalent to that measured with a spectrophotometer, and wireless measurement of salivary turbidity was realized using the mouthguard-type sensor. Based on these results, the proposed mouthguard-type sensor has promising potential for the unconstrained continuous evaluation of oral hygiene.