Multichannel Acoustic Spectroscopy of the Human Body for Inviolable Biometric Authentication.

Specific features of the human body, such as fingerprint, iris, and face, are extensively used in biometric authentication. Conversely, the internal structure and material features of the body have not been explored extensively in biometrics. Bioacoustics technology is suitable for extracting information about the internal structure and biological and material characteristics of the human body. Herein, we report a biometric authentication method that enables multichannel bioacoustic signal acquisition with a systematic approach to study the effects of selectively distilled frequency features, increasing the number of sensing channels with respect to multiple fingers. The accuracy of identity recognition according to the number of sensing channels and the number of selectively chosen frequency features was evaluated using exhaustive combination searches and forward-feature selection. The technique was applied to test the accuracy of machine learning classification using 5,232 datasets from 54 subjects. By optimizing the scanning frequency and sensing channels, our method achieved an accuracy of 99.62%, which is comparable to existing biometric methods. Overall, the proposed biometric method not only provides an unbreakable, inviolable biometric but also can be applied anywhere in the body and can substantially broaden the use of biometrics by enabling continuous identity recognition on various body parts for biometric identity authentication.

Novel electrochemical PMI marker biosensor based on quantum dot dissolution using a double-label strategy.

A novel and facile post-mortem interval (PMI) biosensor was fabricated using a double-label strategy to detect the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) biomarker. A monoclonal anti-GAPDH antibody was immobilized on a surface label containing cadmium selenide quantum dots (CdSe QDs) on a cysteamine graphene oxide (Cys-GO) self-assembled monolayer. Glucose oxidase (GOx) was used as a signal label to conjugate with GAPDH. GAPDH recognition was achieved through the dissolution of the surface-attached CdSe QDs by hydrogen peroxide generated through GAPDH-conjugated GOx-catalyzed ß-glucose oxidation. To enhance sensitivity, a competitive interaction was introduced between free and conjugated GAPDH to the active site of the anti-GAPDH antibody. The electrochemical response due to CdSe dissolution decreased proportionally with the concentration of free GAPDH. Differential pulsed voltammetry was conducted to determine the analytical characteristics of the immunosensor, including the limit of detection, linear dynamic range, target selectivity, system stability, and applicability toward the analysis of real samples.

Electrical Impedance of Upper Limb Enables Robust Wearable Identity Recognition against Variation in Finger Placement and Environmental Factors.

Most biometric authentication technologies commercialized in various fields mainly rely on acquired images of structural information, such as fingerprints, irises, and faces. However, bio-recognition techniques using these existing physical features are always at risk of template forgery threats, such as fake fingerprints. Due to the risk of theft and duplication, studies have recently been attempted using the internal structure and biological characteristics of the human body, including our previous works on the ratiometric biological impedance feature. However, one may still question its accuracy in real-life use due to the artifacts from sensing position variability and electrode-skin interfacing noise. Moreover, since the finger possesses more severe thermoregulatory vasomotion and large variability in the tissue properties than the core of the body, it is necessary to mitigate the harsh changes occurring at the peripheral extremities of the human body. To address these challenges, we propose a biometric authentication method through robust feature extraction from the upper-limb impedance acquired based on a portable wearable device. In this work, we show that the upper limb impedance features obtained from wearable devices are robust against undesirable factors such as finger placement deviations and day-to-day physiological changes, along with ratiometric impedance features. Overall, our upper-limb impedance-based analysis in a dataset of 1627 measurement from 33 subjects lowered the classification error rate from 22.38% to 4.3% (by a factor of 5), and further down to 2.4% (by a factor of 9) when combined with the ratiometric features.

Identity Recognition Based on Bioacoustics of Human Body.

Current biometrics rely on images obtained from the structural information of physiological characteristics, which is inherently a fatal problem of being vulnerable to spoofing. Here, we studied personal identification using the frequency-domain information based on human body vibration. We developed a bioacoustic frequency spectroscopy system and applied it to the fingers to obtain information on the anatomy, biomechanics, and biomaterial properties of the tissues. As a result, modulated microvibrations propagated through our body could capture a unique spectral trait of a person and the biomechanical transfer characteristics persisted for two months and resulted in 97.16% accuracy of identity authentication in 41 subjects. Ultimately, our method not only eliminates the practical means of creating fake copies of the relevant characteristics but also provides reliable features.

Ratiometric Impedance Sensing of Fingers for Robust Identity Authentication.

We present a novel biometric authentication system enabled by ratiometric analysis of impedance of fingers. In comparison to the traditional biometrics that relies on acquired images of structural information of physiological characteristics, our biological impedance approach not only eliminates any practical means of making fake copies of the relevant physiological traits but also provides reliable features of biometrics using the ratiometric impedance of fingers. This study shows that the ratiometric features of the impedance of fingers in 10 different pairs using 5 electrodes at the fingertips can reduce the variation due to undesirable factors such as temperature and day-to-day physiological variations. By calculating the ratio of impedances, the difference between individual subjects was amplified and the spectral patterns were diversified. Overall, our ratiometric analysis of impedance improved the classification accuracy of 41 subjects and reduced the error rate of classification from 29.32% to 5.86% (by a factor of 5).

In vivo Microscopic Photoacoustic Spectroscopy for Non-Invasive Glucose Monitoring Invulnerable to Skin Secretion Products.

Photoacoustic spectroscopy has been shown to be a promising tool for non-invasive blood glucose monitoring. However, the repeatability of such a method is susceptible to changes in skin condition, which is dependent on hand washing and drying due to the high absorption of infrared excitation light to the skin secretion products or water. In this paper, we present a method to meet the challenges of mid-infrared photoacoustic spectroscopy for non-invasive glucose monitoring. By obtaining the microscopic spatial information of skin during the spectroscopy measurement, the skin region where the infrared spectra is insensitive to skin condition can be locally selected, which enables reliable prediction of the blood glucose level from the photoacoustic spectroscopy signals. Our raster-scan imaging showed that the skin condition for in vivo spectroscopic glucose monitoring had significant inhomogeneities and large variability in the probing area where the signal was acquired. However, the selective localization of the probing led to a reduction in the effects of variability due to the skin secretion product. Looking forward, this technology has broader applications not only in continuous glucose monitoring for diabetic patient care, but in forensic science, the diagnosis of malfunctioning sweat pores, and the discrimination of tumors extracted via biopsy.

Synergetic Resonance Matching of a Microphone and a Photoacoustic Cell.

We propose an approach to match the resonant characteristics of a photoacoustic cell with that of a microphone in order to enhance the signal-to-noise ratio in the photoacoustic sensor system. The synergetic resonance matching of a photoacoustic cell and a microphone was achieved by observing that photoacoustic cell resonance is merged with microphone resonance, in addition to conducting numerical and analytical simulations. Using this approach, we show that the signal-to-noise ratio was increased 3.5-fold from the optimized to non-optimized cell in the photoacoustic spectroscopy system. The present work is expected to have a broad impact on a number of applications, from improving weak photoacoustic signals in photoacoustic spectroscopy to ameliorating various sensors that use acoustic resonant filters.

Photoacoustic imaging probe for detecting lymph nodes and spreading of cancer at various depths.

We propose a compact and easy to use photoacoustic imaging (PAI) probe structure using a single strand of optical fiber and a beam combiner doubly reflecting acoustic waves for convenient detection of lymph nodes and cancers. Conventional PAI probes have difficulty detecting lymph nodes just beneath the skin or simultaneously investigating lymph nodes located in shallow as well as deep regions from skin without any supplementary material because the light and acoustic beams are intersecting obliquely in the probe. To overcome the limitations and improve their convenience, we propose a probe structure in which the illuminated light beam axis coincides with the axis of the ultrasound. The developed PAI probe was able to simultaneously achieve a wide range of images positioned from shallow to deep regions without the use of any supplementary material. Moreover, the proposed probe had low transmission losses for the light and acoustic beams. Therefore, the proposed PAI probe will be useful to easily detect lymph nodes and cancers in real clinical fields.

Toxin detection by Si photosensitive biosensors with a new measurement scheme.

We propose a new type of photosensitive biosensor with a CMOS compatible Si photodiode integrated circuit, for the high-sensitive detection of small mycotoxin molecules requiring competitive assay approach. In this work, a photodiode is connected to the gate of a field effect transistor (FET) so that the open circuit voltage (V(OC)) of the illuminated photodiode is transferred into the drain/source current (I(DS)) of the FET. The sensing scheme employs competitive binding of toxin molecules (within the sample solution) and toxin-BSA conjugates (immobilized on the photodiode surface) with Au-nanoparticle-labeled antibodies, followed by silver enhancement to generate opaque structures on the photodiode surface. By utilizing the non-linear dependence of the V(OC) on the light intensity, we can maintain a sufficiently high signal resolution at low toxin concentrations (with most of the incident light blocked) for the competitive assay. By monitoring the I(DS) of the FET whose gate is driven by the V(OC), quantitative detection of Aflatoxin B1 has been achieved in the range of 0-15ppb.

CMOS image sensor for detection of interferon gamma protein interaction as a point-of-care approach.

Complementary metal oxide semiconductor (CMOS)-based image sensors have received increased attention owing to the possibility of incorporating them into portable diagnostic devices. The present research examined the efficiency and sensitivity of a CMOS image sensor for the detection of antigen-antibody interactions involving interferon gamma protein without the aid of expensive instruments. The highest detection sensitivity of about 1 fg/ml primary antibody was achieved simply by a transmission mechanism. When photons are prevented from hitting the sensor surface, a reduction in digital output occurs in which the number of photons hitting the sensor surface is approximately proportional to the digital number. Nanoscale variation in substrate thickness after protein binding can be detected with high sensitivity by the CMOS image sensor. Therefore, this technique can be easily applied to smartphones or any clinical diagnostic devices for the detection of several biological entities, with high impact on the development of point-of-care applications.

Complementary metal-oxide semiconductor (CMOS) image sensor: an insight as a point-of-care label-free immunosensor.

The present paper examines the efficiency of a complementary metal-oxide semiconductor (CMOS) using an indium nanoparticle (InNP) substrate for the high-sensitivity detection of antigen/antibody interactions at concentrations as low as 100 pg/ml under normal light. Metal NPs coated with antigen/antibody layers act as a dielectric layer on the conducting sphere, which enhances the number of photons hitting the sensor surface through a light-scattering effect. This photon number is proportional to the digital number observed with the CMOS sensor for detecting antigen/antibody interactions.

Direct label-free electrical immunodetection in human serum using a flow-through-apparatus approach with integrated field-effect transistors.

In order to identify changes in the levels of key proteins in response to the onset or development of a disease, the research fields of proteomics and genomics seek to develop new biomarkers. Specifically, simple and fast biomarker screens have a central role in many areas of healthcare, including disease diagnosis and drug discovery. Biologically modified field-effect transistor (BioFET) is one of the most attractive approaches because of the on-chip integration of the sensor array, fast response, high reliability and low-cost mass production. However, the BioFETs used to detect macromolecules have been operated only in buffer solution with low salt concentrations because of the Debye screening length of blood or serum. Here we report a novel detection technique for direct label-free immunodetection of cancer markers in human serum using a Si-FET that was fabricated by conventional photolithographic processes. The proposed sensing method shows no dissociation of antigen-antibody binding as in general immunoassays, unlike the previous reports on Si-FET sensors. This method therefore overcomes the Debye length problem of immunodetection in human fluids, such as serum, that are generally encountered by FET-based biosensors. Our results demonstrate specific label-free and real-time immunodetection of a cancer marker at a concentration of 0.2 ng/mL in human serum, quantitative detection of the marker from 0.2 to 114 ng/mL, and successful multiplexed sensing of three different cancer markers. We believe that connecting our simple electrical detection method, which does not require pretreatment of serum, with well-established whole blood filter technology will contribute to the development of new point-of-care testing (POCT) sensors.

Control of channel doping concentration for enhancing the sensitivity of 'top-down' fabricated Si nanochannel FET biosensors.

The sensitivity of 'top-down' fabricated Si nanochannel field effect transistor (FET) biosensors has been analyzed quantitatively, as a function of the channel width and doping concentration. We have fabricated 130-, 150-, and 220 nm-wide Si FET channels with 40 nm-thick p-type silicon-on-insulator (SOI) layers doped at 8 x 10(17) and 2 x 10(18) cm(-3), and characterized their sensitivity in response to the variation of surface charges as hydrogen ion sensors within buffer solutions of various pH levels. Within the range of channel width and doping concentration investigated, the pH sensitivity of Si channels is enhanced much more effectively by decreasing the doping concentration than by reducing the channel width, which suggests a practical strategy for achieving high sensitivity with less effort than to reduce the channel width. Similar behavior has also been confirmed in the immunodetection of prostate specific antigen (PSA). Combined with excellent reproducibility and uniformity of the channel structure, high controllability of the doping concentration can make the 'top-down' fabrication a very useful approach for the massive fabrication of high-sensitivity sensor platforms in a cost-effective way.