Spicy Recipe for At-Home Diagnostics: Smart Salivary Sensors for Point-of-Care Diagnosis of Jaundice.

Even though significant advances have been made, there is still a lack of reliable sensors capable of noninvasively monitoring bilirubin and diagnosing jaundice as the most common neonatal disease, particularly at the point-of-care (POC) where blood sampling from infants is accompanied by serious challenges and concerns. Herein, for the first time, using an easy-to-fabricate/use assay, we demonstrate the capability of curcumin embedded within paper for noninvasive optical monitoring of bilirubin in saliva. The highly selective sensing of the developed sensor toward bilirubin is attributed to bilirubin photoisomerization under blue light exposure, which can selectively restore the bilirubin-induced quenched fluorescence of curcumin. We also fabricated an IoT-enabled hand-held optoelectronic reader to measure and quantify the fluorescence and color signals of our sensor. Clinical analysis on the saliva of 18 jaundiced infants by using our developed smart salivary sensor proved that it is amenable to be widely exploited in POC applications for bilirubin monitoring as there are good correlations between its results with those of reference methods in saliva and blood. Meeting all WHO's REASSURED criteria by our developed sensor makes it a highly promising sensor for smart noninvasive diagnosis and therapeutic monitoring of jaundice, hepatitis, and other bilirubin-induced neurologic diseases at the POC.

Smart Wearable Nanopaper Patch for Continuous Multiplexed Optical Monitoring of Sweat Parameters.

Notwithstanding the substantial progress in optical wearable sensing devices, developing wearable optical sensors for simultaneous, real-time, and continuous monitoring of multiple biomarkers is still an important, yet unmet, demand. Aiming to address this need, we introduced for the first time a smart wearable optical sensor (SWOS) platform combining a multiplexed sweat sensor sticker with its IoT-enabled readout module. We employed our SWOS system for on-body continuous, real-time, and simultaneous fluorimetric monitoring of sweat volume (physical parameter) and pH (chemical marker). Herein, a variation in moisture (5-45 µL) or pH (4.0-7.0) causes a color/fluorescence change in the copper chloride/fluorescein immobilized within a transparent chitin nanopaper (ChNP) in a selective and reversible manner. Human experiments conducted on athletic volunteers during exercise confirm that our developed SWOS platform can be efficiently exploited for smart perspiration analysis toward personalized health monitoring. Moreover, our system can be further extended for the continuous and real-time multiplexed monitoring of various biomarkers (metabolites, proteins, or drugs) of sweat or other biofluids (for example, analyzing exhaled breath by integrating onto a facemask).

Moving toward smart biomedical sensing.

The development of novel biomedical sensors as highly promising devices/tools in early diagnosis and therapy monitoring of many diseases and disorders has recently witnessed unprecedented growth; more and faster than ever. Nonetheless, on the eve of Industry 5.0 and by learning from defects of current sensors in smart diagnostics of pandemics, there is still a long way to go to achieve the ideal biomedical sensors capable of meeting the growing needs and expectations for smart biomedical/diagnostic sensing through eHealth systems. Herein, an overview is provided to highlight the importance and necessity of an inevitable transition in the era of digital health/Healthcare 4.0 towards smart biomedical/diagnostic sensing and how to approach it via new digital technologies including Internet of Things (IoT), artificial intelligence, IoT gateways (smartphones, readers), etc. This review will bring together the different types of smartphone/reader-based biomedical sensors, which have been employing for a wide variety of optical/electrical/electrochemical biosensing applications and paving the way for future eHealth diagnostic devices by moving towards smart biomedical sensing. Here, alongside highlighting the characteristics/criteria that should be met by the developed sensors towards smart biomedical sensing, the challenging issues ahead are delineated along with a comprehensive outlook on this extremely necessary field.

Corrigendum to "Toward smart diagnosis of pandemic infectious diseases using wastewater-based epidemiology" [Trac. Trends Anal. Chem. 153 (2022) 116635].

[This corrects the article DOI: 10.1016/j.trac.2022.116635.].

Toward smart diagnosis of pandemic infectious diseases using wastewater-based epidemiology.

COVID-19 outbreak revealed fundamental weaknesses of current diagnostic systems, particularly in prediction and subsequently prevention of pandemic infectious diseases (PIDs). Among PIDs detection methods, wastewater-based epidemiology (WBE) has been demonstrated to be a favorable mean for estimation of community-wide health. Besides, by going beyond purely sensing usages of WBE, it can be efficiently exploited in Healthcare 4.0/5.0 for surveillance, monitoring, control, and above all prediction and prevention, thereby, resulting in smart sensing and management of potential outbreaks/epidemics/pandemics. Herein, an overview of WBE sensors for PIDs is presented. The philosophy behind the smart diagnosis of PIDs using WBE with the help of digital technologies is then discussed, as well as their characteristics to be met. Analytical techniques that are pushing the frontiers of smart sensing and have a high potential to be used in the smart diagnosis of PIDs via WBE are surveyed. In this context, we underscore key challenges ahead and provide recommendations for implementing and moving faster toward smart diagnostics.

On-Site Detection of Carcinoembryonic Antigen in Human Serum.

Real-time connectivity and employment of sustainable materials empowers point-of-care diagnostics with the capability to send clinically relevant data to health care providers even in low-resource settings. In this study, we developed an advantageous kit for the on-site detection of carcinoembryonic antigen (CEA) in human serum. CEA sensing was performed using cellulose-based lateral flow strips, and colorimetric signals were read, processed, and measured using a smartphone-based system. The corresponding immunoreaction was reported by polydopamine-modified gold nanoparticles in order to boost the signal intensity and improve the surface blocking and signal-to-noise relationship, thereby enhancing detection sensitivity when compared with bare gold nanoparticles (up to 20-fold in terms of visual limit of detection). Such lateral flow strips showed a linear range from 0.05 to 50 ng/mL, with a visual limit of detection of 0.05 ng/mL and an assay time of 15 min. Twenty-six clinical samples were also tested using the proposed kit and compared with the gold standard of immunoassays (enzyme linked immunosorbent assay), demonstrating an excellent correlation (R = 0.99). This approach can potentially be utilized for the monitoring of cancer treatment, particularly at locations far from centralized laboratory facilities.

Toward Smart Diagnostics in a Pandemic Scenario: COVID-19.

The incredible spread rate of coronavirus disease 2019 (COVID-19) outbreak has shocked the world. More than ever before, this dramatic scenario proved the significance of diagnostics as a cornerstone to make life-saving decisions. In this context, novel diagnostics that generates smart data leading to superior strategies for treatment, control, surveillance, prediction, prevention, and management of pandemic diseases is vital. Herein, we discuss the characteristics that should be met by COVID-19 diagnostics to become smart diagnostics enabled by industry 4.0 especially Internet of Things (IoT). The challenges ahead and our recommendations for moving faster from pure diagnostics toward smart diagnostics of COVID-19 and other possible epidemic/pandemic diseases are also outlined. An IoT-Fog-Cloud model based on smartphones as IoT gateways for smart diagnostics with unified strategies for data collection/transmission/interpretation is also proposed to integrate new digital technologies into a single platform for smarter decisions. Last but not least, we believe that "smart diagnostics" is a perspective that should be realized sooner before we encounter a pandemic far worse than the present one.

(Nano)tag-antibody conjugates in rapid tests.

Antibodies (Abs) are naturally derived materials with favorable affinity, selectivity, and fast binding kinetics to the respective antigens, which enables their application as promising recognition elements in the development of various types of biosensors/bioassays, especially in rapid tests. These tests are low-cost and easy-to-use biosensing devices with broad applications including medical or veterinary diagnostics, environmental monitoring and industrial usages such as safety and quality analysis in food, providing on-site quick monitoring of various analytes, making it possible to save analysis costs and time. To reach such features, the conjugation of Abs with various nanomaterials (NMs) as tags is necessary, which range from conventional gold nanoparticles to other nanoparticles recently introduced, where magnetic, plasmonic, photoluminescent, or multi-modal properties play a critical role in the overall performance of the analytical device. In this context, to preserve the Ab affinity and provide a rapid response with long-term storage capability, the use of efficient bio-conjugation techniques is critical. Thanks to their prominent role in rapid tests, many studies have been devoted to the design and development of Abs-NMs conjugates with various chemistries including passive adsorption, covalent coupling, and affinity interactions. In this review, we present the state-of-the-art techniques allowing various Ab-NM conjugates with a special focus on the efficiency of the developed probes to be employed in in vitro rapid tests. Challenges and future perspectives on the development of Ab-conjugated nanotags in rapid diagnostic tests are highlighted along with a survey of the progress in commercially available Ab-NM conjugates.

Phytochemicals toward Green (Bio)sensing.

Because of numerous inherent and unique characteristics of phytochemicals as bioactive compounds derived from plants, they have been widely used as one of the most interesting nature-based compounds in a myriad of fields. Moreover, a wide variety of phytochemicals offer a plethora of fascinating optical and electrochemical features that pave the way toward their development as optical and electrochemical (bio)sensors for clinical/health diagnostics, environmental monitoring, food quality control, and bioimaging. In the current review, we highlight how phytochemicals have been tailored and used for a wide variety of optical and electrochemical (bio)sensing and bioimaging applications, after classifying and introducing them according to their chemical structures. Finally, the current challenges and future directions/perspective on the optical and electrochemical (bio)sensing applications of phytochemicals are discussed with the goal of further expanding their potential applications in (bio)sensing technology. Regarding the advantageous features of phytochemicals as highly promising and potential biomaterials, we envisage that many of the existing chemical-based (bio)sensors will be replaced by phytochemical-based ones in the near future.

Towards smart personalized perspiration analysis: An IoT-integrated cellulose-based microfluidic wearable patch for smartphone fluorimetric multi-sensing of sweat biomarkers.

Practical obstacles, such as intricate designs and expensive equipment/materials, in the fabrication of wearable sweat sensors, have limited their feasibility as a personalized healthcare device. Herein, we have fabricated a cellulose-based wearable patch, which further paired with a smartphone-based fluorescence imaging module and a self-developed smartphone app for non-invasive and in situ multi-sensing of sweat biomarkers including glucose, lactate, pH, chloride, and volume. The developed Smart Wearable Sweat Patch (SWSP) sensor comprises highly fluorescent sensing probes embedded in paper substrates, and microfluidic channels consisted of cotton threads to harvest sweat from the skin surface and to transport it to the paper-based sensing probes. The imaging module was fabricated by a 3D printer, equipped with UV-LED lamps and an optical filter to provide the in situ capability of capturing digital images of the sensors via a smartphone. A smartphone app was also designed to quantify the concentration of the biomarkers via a detection algorithm. Additionally, we have recommended an Internet of Things (IoT)-based model for our developed SWSP sensor to promote its potential application for the future. The field studies on human subjects were also conducted to investigate the feasibility of our developed SWSP sensor for the analysis of sweat biomarkers. Our findings convincingly demonstrated the applicability of our developed SWSP sensor as a smart, user-friendly, ultra-low-cost (~0.03 $ per sweat patch), portable, selective, rapid, and non-invasive healthcare monitoring device for immense applications in health personalization, sports performance monitoring, and medical diagnostics.

Nanopaper-based screen-printed electrodes: a hybrid sensing bioplatform for dual opto-electrochemical sensing applications.

Given the importance of developing easy-to-use, disposable, affordable, and portable hybrid opto-electrochemical sensing devices, for the first time, we have developed a nanopaper-based screen-printed electrode (SPE) by taking advantage of the high optical transparency, affordability, biocompatibility, printability, flexibility, and other unrivaled physicochemical properties of bacterial cellulose (BC) nanopaper in screen printing technology. To fabricate the BC-SPE platform, a screen-printed three-electrode system was transferred onto the dried film of a pre-printed BC nanopaper-based substrate. Because of the optical transparency of the BC nanopaper, the fabricated BC-SPE platform can be used as a hybrid sensing platform for simultaneous optical and electrochemical (bio)sensing applications. A portable photometer was also assembled to measure the optical signals of the fabricated BC-SPE. The opto-electrochemical tunable properties of Prussian blue and their application in the dual optical and electrochemical sensing of acetaminophen as a model analyte were investigated using the fabricated BC-SPE to demonstrate the sensing applicability of the developed hybrid bioplatform. Moreover, we prove that our fabricated BC-SPE can be potentially exploited as a smartphone-based electrochemiluminescence (ECL) sensing platform. We envisage that our developed BC-SPE platform will find promising practical application in the detection of a wide range of (bio)chemicals, and also would be inspirational for the development of novel hybrid opto-electrochemical (bio)sensing devices.

A Green Chemosensor for Colorimetric Determination of Phosphate Ion in Soil, Bone, and Water Samples Using Curcumin Nanoparticles.

This article presents a sensitive and straightforward colorimetric chemosensor for the determination of phosphate ion utilizing curcumin nanoparticles (CUNPs) as the sensing system. The color of as-prepared CUNPs can be changed from yellow to orange upon adding iron(III) ions due to the formation of a complex with CUNPs. However, in the presence of phosphate ions, iron(III) ions prefer to bind to phosphate ions and, subsequently the color of CUNPs is selectively recovered because of releasing the iron(III) ions from the CUNPs-iron(III) complex. Therefore, in this work the selective color changing of the CUNPs-iron(III) system upon the addition of phosphate ions was used for the quantitative sensing of phosphate ions. Various factors, such as the pH, concentration of iron(III) and volume of CUNPs, were examined and the optimum conditions were established. A linear calibration graph over the range of 10 - 400 ng mL-1 for phosphate (r = 0.9995) was achieved using the optimal conditions. The limit of detection (LOD) of the proposed method for phosphate was 7.1 ng mL-1 and the relative standard deviation (RSD) for measuring 50 ng mL-1 of phosphate was 3.7% (n = 8). The developed method was applied for the measurement of phosphate in water, soil, and bone samples. Satisfactory results were obtained.

Chitin Nanofiber Paper toward Optical (Bio)sensing Applications.

Because of numerous inherent and unrivaled features of nanofibers made of chitin, the second most plentiful natural-based polymer (after cellulose), including affordability, abundant nature, biodegradability, biocompatibility, commercial availability, flexibility, transparency, and extraordinary mechanical and physicochemical properties, chitin nanofibers (ChNFs) are being applied as one of the most appealing bionanomaterials in a myriad of fields. Herein, we exploited the beneficial properties offered by the ChNF paper to fabricate transparent, efficient, biocompatible, flexible, and miniaturized optical sensing bioplatforms via embedding/immobilizing various plasmonic nanoparticles (silver and gold nanoparticles), photoluminescent nanoparticles (CdTe quantum dots, carbon dots, and NaYF4:Yb3+@Er3+&SiO2 upconversion nanoparticles) along with colorimetric reagents (curcumin, dithizone, etc.) in the 3D nanonetwork scaffold of the ChNF paper. Several configurations, including 2D multi-wall and 2D cuvette patterns with hydrophobic barriers/walls and hydrophilic test zones/channels, were easily printed using laser printing technology or punched as spot patterns on the dried ChNF paper-based nanocomposites to fabricate the (bio)sensing platforms. A variety of (bio)chemicals as model analytes were used to confirm the efficiency and applicability of the fabricated ChNF paper-based sensing bioplatforms. The developed (bio)sensors were also coupled with smartphone technology to take the advantages of smartphone-based monitoring/sensing devices along with the Internet of Nano Things (IoNT)/the Internet of Medical Things (IoMT) concepts for easy-to-use sensing applications. Building upon the unrivaled and inherent features of ChNF as a very promising bionanomaterial, we foresee that the ChNF paper-based sensing bioplatforms will emerge new opportunities for the development of innovative strategies to fabricate cost-effective, simple, smart, transparent, biodegradable, miniaturized, flexible, portable, and easy-to-use (bio)sensing/monitoring devices.

A nanocellulose-based colorimetric assay kit for smartphone sensing of iron and iron-chelating deferoxamine drug in biofluids.

The current work describes the development of a "nanopaper-based analytical device (NAD)", through the embedding of curcumin in transparent bacterial cellulose (BC) nanopaper, as a colorimetric assay kit for monitoring of iron and deferoxamine (DFO) as iron-chelating drug in biological fluids such as serum blood, urine and saliva. The iron sensing strategy using the developed assay kit is based on the decrease of the absorbance/color intensity of curcumin-embedded in BC nanopaper (CEBC) in the presence of Fe(III), due to the formation of Fe(III)-curcumin complex. On the other hand, releasing of Fe(III) from Fe(III)-CEBC upon addition of DFO as an iron-chelating drug, due to the high affinity of this drug to Fe(III) in competition with curcumin, which leads to recovery of the decreased absorption/color intensity of Fe(III)-CEBC, is utilized for selective colorimetric monitoring of this drug. The absorption/color changes of the fabricated assay kit as output signal can be monitored by smartphone camera or by using a spectrophotometer. The results of our developed sensor agreed well with the results from a clinical reference method for determination of Fe(III) concentration in human serum blood samples, which revealed the clinical applicability of our developed assay kit. Taken together, regarding the advantageous features of the developed sensor as an easy-to-use, non-toxic, disposable, cost-effective and portable assay kit, along with those of smartphone-based sensing, it is anticipated that this sensing bioplatform, which we name lab-on-nanopaper, will find utility for sensitive, selective and easy diagnosis of iron-related diseases (iron deficiency and iron overload) and therapeutic drug monitoring (TDM) of iron-chelating drugs in clinical analysis as well.

Spectrophotometric and visual determination of zoledronic acid by using a bacterial cell-derived nanopaper doped with curcumin.

A nanopaper-based analytical device (NAD) is described for a colorimetric metal-complexing indicator-displacement assay (M-IDA) for zoledronic acid (ZA). Bacterial cellulose nanopaper was doped with curcumin to obtain a chemosensor on which hydrophilic test zones were patterned via laser printing of hydrophobic walls. The color intensity of the test zones decreases in the presence of Fe(III) due to the formation of Fe(III)-curcumin complex. However, upon addition of ZA, Fe(III) ions preferably binds ZA. Subsequently, the color of the zone changes from light yellow to dark yellow. The changes in the absorption (measured at 427 nm) and of the color of the test stripe can be monitored visually, by using a digital camera, or by a spectrophotometer. Under optimal conditions, the analytical signals increase linearly in the 0.01-100 µM ZA concentration range, and the detection limits are 8.8 and 8.0 nM for smartphone and spectrophotometer-based methods, respectively. The method was employed to the determination of ZA in (spiked) urine, serum, saliva, and in pharmaceutical samples. Graphical abstract Schematic representation of a nanopaper-based analytical device based on curcumin-doped BC nanopaper (CDBC) integrated with smartphone for metal-complexing indicator-displacement assay of zoledronic acid (ZA). High affinity of ZA to Fe(III) on the NAD/CDBC leads to color change.

Lab-on-nanopaper: An optical sensing bioplatform based on curcumin embedded in bacterial nanocellulose as an albumin assay kit.

Herein, we introduce a nanopaper-based analytical device (NAD) or "lab-on-nanopaper" device for visual sensing of human serum albumin (HSA) in human blood serums, which relies on embedding of curcumin within transparent bacterial cellulose (BC) nanopaper. BC nanopaper is an appropriate candidate to be an excellent platform for the development of optical (bio)sensors due to having exceptional properties such as optical transparency, high flexibility, porosity, biodegradability, and printability. The hydrophilic test zones were created on the fabricated bioplatform through creating the hydrophobic walls via laser printing technology. The color changes of curcumin embedded in BC nanopaper (CEBC) due to the inhibitory effect of HSA on the curcumin degradation in alkaline solutions, which can be monitored visually (naked eye/Smartphone camera) or spectroscopically using a spectrophotometer, were linearly proportional to the HSA concentration in the range of 10-300 µM and 25-400 µM, respectively. The developed NAD/CEBC as a novel albumin assay kit was successfully utilized to the determination of HSA in human blood serum samples with satisfactory results. Building upon the fascinating features of BC nanopaper as a very promising bioplatform in optical (bio)sensing applications we are confident "lab-on-nanopaper" devices/NADs, which take the advantages of the nanopaper and also meet the ASSURED criteria, could be considered as a new generation of optical (bio)sensing platforms that are currently based on paper, glass or plastic substrates.

Easy Diagnosis of Jaundice: A Smartphone-Based Nanosensor Bioplatform Using Photoluminescent Bacterial Nanopaper for Point-of-Care Diagnosis of Hyperbilirubinemia.

One of the concerns of parents in the first days of their baby's birth is the baby's risk of jaundice/hyperbilirubinemia. This is because more than 60% of babies are born with jaundice that, if not timely diagnosed and subsequently treated, can lead to serious damage to their health. On the other hand, despite recent progress in sensor technology for clinical applications, the development of easy-to-use, cost-effective, sensitive, specific, and portable diagnostic devices, which use nontoxic and biodegradable materials in their design and fabrication, is still in high demand. Herein we present an easy-to-use, cost-effective, selective, nontoxic, and disposable photoluminescent nanopaper-based assay kit with a smartphone readout for easy diagnosis of neonatal jaundice through visual determination of Bilirubin (BR) in infants' blood samples. The developed BR assay kit comprises highly photoluminescent carbon dot (CD) sensing probes embedded in a bacterial cellulose (BC) nanopaper substrate (CDBN). The photoluminescence (PL) of the developed BR sensor is quenched in the presence of BR as a PL quencher and then selectively recovered upon blue light (λ = 470 nm) exposure, due to conversion of the unconjugated BR to the colorless oxidation products (non-PL quencher) through BR photoisomerization and photooxidation, that subsequently leads to selective PL enhancement of CDBN. The recovered PL intensity of the developed BR assay kit, which was monitored by integrated smartphone camera, was linearly proportional to the concentration of BR in the range of 2-20 mg dL-1. The feasibility of real application of the fabricated smartphone-based BR assay kit was also confirmed via comparing the results of our method with a clinical reference method for determination of BR concentration in infant's blood samples. With the advantages of nontoxicity and the extraordinary physicochemical properties of photoluminescent BC nanopaper as the sensing substrate, along with those of smartphone technology, we believe that our developed smartphone-based BR assay kit, as an easy-to-use, cost-effective (∼0.01 Euro per test), portable and novel sensing bioplatform, can be potentially exploited for sensitive, specific, rapid, and easy BR detection and jaundice diagnosis at the point of care (POC) and in routine clinical laboratories as well.

A paper-based optical probe for chromium by using gold nanoparticles modified with 2,2'-thiodiacetic acid and smartphone camera readout.

A paper based analytical device is presented for the determination of Cr(III) and Cr(VI) using gold nanoparticles (AuNPs) modified with 2,2'-thiodiacetic acid. The modified AuNPs were characterized using UV-Vis spectrophotometry, Fourier transform infrared, dynamic light scattering, zeta potential, energy dispersive spectroscopy and transmission electron microscopy. Cr(III) ions induce the aggregation of the modified AuNPs, and the color of the nanoprobe changes from red to blue. This can be detected visually, or by colorimetry, or with a camera. No interference is observed in the presence of 19 other cations and anions. Cr(VI) (chromate) can be determined by after reduction to Cr(III) by using ascorbic acid and then quantified total Cr(III). The concentration of Cr(VI) is obtained by subtracting the concentration of Cr(III) from that of total chromium. Under optimal conditions, the ratio of the absorbances measured at 670 (blue) and 522 (red) increases linearly in the 1.0 nM to 22.1 µM chromium concentration range, with 0.66 nM (0.034 ppb) limit of detection (LOD) in solution. In case of the paper device, the linear range extends from 1.0 nM to 0.1 mM, and the LOD is 0.64 nM (0.033 ppb). The method was applied to the determination of chromium in spiked water, urine and dilutes human plasma, and results were confirmed by GF-AAS analysis. This method is highly selective, fast and portable, requires minimum volume of reagents and samples and no washing steps. Graphical abstract A paper based analytical device is presented for determination of Cr(III) and Cr(VI) using gold nanoparticles modified with 2,2'-thiodiacetic acid. In paper optical probe, linear range and limit of detection are 1.0 nM to 0.1 mM and 0.64 nM, respectively. The method was applied to the determination of total chromium in spiked water, urine and dilutes human plasma, and results were confirmed by GF-AAS analysis.

A rainbow ratiometric fluorescent sensor array on bacterial nanocellulose for visual discrimination of biothiols.

Considering the crucial role of biothiols in many biological processes, which turns them into highly valuable biomarkers for the early diagnosis of various diseases, the development of an affordable, sensitive and portable probe for the identification and discrimination of these compounds is of great importance. Herein, we developed a ratiometric fluorescent (RF) sensor array with a wide color emissive variation, on a bacterial cellulose (BC) nanopaper substrate for the visual discrimination of biothiols. To this aim, RF sensing elements including N-acetyl l-cysteine capped green CdTe quantum dots-rhodamine B (GQDs-RhB) and red CdTe QDs-carbon dots (RQDs-CDs) at two different NaOH concentrations (0 and 5 mM) were utilized as sensor elements for the discrimination of biothiols. Owing to the high affinity of the thiol group (SH) to the surface of CdTe QDs and the aggregation of the QDs, the fluorescence (FL) emission of the QDs changed while the emission of the CDs and rhodamine B remained almost unchanged upon the addition of biothiols. Accordingly, characteristic rainbow-like FL fingerprint patterns were created for each biothiol which were then distinguished both visually and spectroscopically. Hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA) pattern recognition techniques were employed for the identification and discrimination of biothiols. Based on the designed RF sensor array, convenient test strips were fabricated on BC nanopaper for the visual discrimination of biothiols. It has been shown that this probe can successfully identify biothiols in human plasma as well. Altogether, the developed nanopaper-based sensor array offers an efficient biothiol discrimination tool that can be potentially exploited in the near future in theranostic and point-of-care applications.

A nanopaper-based artificial tongue: a ratiometric fluorescent sensor array on bacterial nanocellulose for chemical discrimination applications.

In the present study, a ratiometric fluorescent sensor array as an artificial tongue has been developed on a nanopaper platform for chemical discrimination applications. The bacterial cellulose (BC) nanopaper was utilized for the first time as a novel, flexible, and transparent substrate in the optical sensor arrays for developing high-performance artificial tongues. To fabricate this platform, the hydrophobic walls on the BC nanopaper substrates were successfully created using a laser printing technology. In addition, we have used the interesting photoluminescence (PL) properties of an immobilized ratiometric probe (carbon dot-Rhodamine B (CD-RhB) nanohybrids) on the nanopaper platform to improve the visual discrimination analysis. Heavy metal ions were utilized as model analytes to verify the applicability of the fabricated nanopaper-based ratiometric fluorescent sensor array (NRFSA). Using the color variation of the NRFSA platform upon the addition of heavy metal ions, which have been obtained by a smartphone (under an UV irradiation), five heavy metal ions (i.e., Hg(ii), Pb(ii), Cd(ii), Fe(iii), and Cu(ii)) have been well-distinguished through the RGB analysis via production of the characteristic PL fingerprint-like response patterns for each of them. Moreover, the developed optical sensor array was successfully exploited to identify the heavy metal ions in the water and fish samples. We have also found that the PL spectra, which have been obtained by a spectrofluorometer, of the developed NRFSA can be exploited for discrimination applications. We believe that the nanopaper-based artificial tongues will provide innovative insights into the development of optical sensor arrays towards advanced (bio)chemical discrimination applications and can revolutionize the conventional optical sensor array technology.