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Although CRISPR-based nucleic acid detection has great potential in point-of-care testing due to its simplicity, it has been rarely integrated into paper-based analytical devices (PADs), which are attractive platforms to simplify assays. This work introduces a CRISPR-assisted nucleic acid quantification approach integrated into a PAD with signal readout by a personal glucose meter (PGM). Retention of magnetic beads by filter paper and pre-deposition of all required reagents by freeze-drying stabilized with trehalose enabled the indirect quantification of human papilloma virus (HPV) DNA through a PGM readout without complicated user intervention and complex reagent handling. The calculated limit of detection was 57 pM, which is comparable with other amplification-free CRISPR-based assays detecting nucleic acids. The fully integrated device exhibited good storage stability for up to 4 weeks, suggesting its applicability toward practical point-of-care nucleic acid quantification.

The first step in blood testing necessitates blood separation to obtain an adequate volume of plasma. Traditional centrifugation is bulky, expensive and electricity-powered, which is not suitable for micro-scale blood plasma separation in point-of-care testing (POCT) cases. Microfluidic paper-based plasma separation devices present a promising alternative for plasma separation in such occasions. However, they are limited in terms of plasma yield, which hinders analyte detection. Herein, we proposed a humidity-enhanced paper-based microfluidic plasma separation method to address this issue. Specifically, paper was first treated by blood-typing antibodies, then samples of whole blood were introduced into the prepared paper. After waiting for 5 min for RBC agglutination and plasma wicking under high humidity, micro-scale plasma separation from whole blood was achieved. As a result, an extremely high plasma yield of up to 60.1% could be separated from whole blood through using Xuan-paper. Meanwhile, the purity of plasma could reach 99.99%. Finally, this innovative approach was effortlessly integrated into distance-based glucose concentration detection, enabling rapid determination of blood glucose levels through naked-eye observation. Considering the simplicity and inexpensiveness of this method, we believe that this technology could be integrated to more paper-based microfluidic analytical devices for rapid and accurate detection of plasma analytes in POCT.

A novel microfluidic paper-based analytical device with dual colorimetric and electrochemical detection (dual μPAD) was developed for the assessment of transferrin saturation (TSAT) in samples from ischemic stroke patients. TSAT was calculated from the ratio between transferrin-bound iron, which was colorimetrically measured, and the total iron-binding capacity, which was electrochemically measured. To this end, a μPAD was smartly designed, which integrated both colorimetric and electrochemical detection reservoirs, communicating via a microchannel acting as a chemical reactor, and with preloading/storing capabilities (reagent-free device). This approach allowed the dual and simultaneous determination of both parameters, providing an improvement in the reliability of the results due to an independent signal principle and processing. The μPADs were validated by analyzing a certified reference material, showing excellent accuracy ( E r ≤ 5%) and precision (RSD ≤ 2%). Then they were applied to the analysis of diagnosed serum samples from ischemic stroke patients. The results were compared to those provided by a free-interference method (urea-PAGE). Impressively, both methods exhibited a good correlation ( r = 0.96, p < 0.05) and no significant differences were found between them (slope 1.0 ± 0.1 and the intercept 1 ± 4, p < 0.05), demonstrating the excellent accuracy of our approach during the analysis of complex samples from ischemic stroke patients, using just 90 μL of clinical samples and taking less than 90 min in comparison with the 18 hours required by the urea-PAGE approach. The developed fully integrated colorimetric-electrochemical μPAD is a promising ready to use reagent-free device for the point-of-care testing of TSAT, which can be used to assist physicians in the fast diagnosis and prognosis of ischemic strokes, where the decision-time is crucial for the patient's survival.

Paper-based analytical devices (PADs) are very convenient for determining biomarkers in point-of-care (POC) diagnosis while requiring sample pre-treatment or impurity separation. This study reports a novel hydrogel-coupled, paper-based analytical device (PAD) for separation-free H 2 O 2 colorimetric detection in both aqueous solution and cell lysis with sample-to-answer analysis by directly loading into the sample test zone. By encapsulating an inorganic mimic enzyme and chromogenic substrate into the sodium alginate (SA) hydrogel, amplification of the color signal after catalyzing the substrate could be achieved. Taking advantage of the nanoscale porous structure of the hydrogel and the lateral flow channel of the PAD, large interference fragments or bio-macromolecules are prevented from diffusing into the chromogenic reaction, whereas the small target molecules enter the sensing region to trigger the catalytic reaction. This method demonstrated a rapid and accurate analysis with a limit of detection as low as 0.06 mM and detection selectivity. Our proposed device requires no enzyme and is separation-free, portable, easy-to-fabricate, and low-cost, and may offer a platform for quantitative or qualitative analysis of other analytes in body fluids for POC applications.

Paper-based rapid diagnostic tests (RDTs) are an essential component of modern healthcare, particularly for the management of infectious diseases. Despite their utility, these capillary-driven RDTs are compromised by high failure rates, primarily caused by user error. This limits their utility in complex assays that require multiple user operations. Here, we demonstrate how this issue can be directly addressed through continuous electrochemical monitoring of reagent flow inside an RDT using embedded graphenized electrodes. Our method relies on applying short voltage pulses and measuring variations in capacitive discharge currents to precisely determine the flow times of injected samples and reagents. This information is reported to the user, guiding them through the testing process, highlighting failure cases and ultimately decreasing errors. Significantly, the same electrodes can be used to quantify electrochemical signals from immunoassays, providing an integrated solution for both monitoring assays and reporting results. We demonstrate the applicability of this approach in a serology test for the detection of anti-SARS-CoV-2 IgG in clinical serum samples. This method paves the way towards "smart" RDTs able to continuously monitor the testing process and improve the robustness of point-of-care diagnostics.

Nowadays, kidney dysfunction is a common health issue due to the modernized lifestyle. Even though medications are commercially available to treat kidney diseases, early diagnosis is crucial and challenging. Clinically, measuring urine creatinine and pH has gained significant interest as a way to diagnose kidney diseases early. In the present work, we attempted to develop a low-cost, robust, accurate and naked-eye colorimetric method to determine both creatinine levels and pH variations in artificial urine samples using a simple 3D-printed hybrid microfluidic device. Creatinine was detected by the incorporation of the traditional Jaffe test onto the hybrid paper-PMMA microfluidic device and pH (4-8) was measured by a simple anthocyanin test. Notably, the tests were established without employing any sophisticated or costly instrument clusters. The developed 3D-printed microfluidic probe showed a limit of detection (LOD) of 0.04 mM for creatinine over a concentration range of 1-10 mM, with a regression coefficient ( R 2 ) of 0.995 in laboratory conditions. Interestingly, the experimental data obtained with artificial urine exhibited a wide linear range from 0.1 mM to 5 mM under different pH values ranging from 4 to 8 in the presence of matrices commonly found in urine samples other than proteins, indicating the potential use of this method in pre-clinical analysis. Since the wide linear range of urine creatinine in artificial urine samples falls well below the clinically relevant concentrations in humans (0.07-0.27 mM), the developed lab-on-chip device is further suitable for clinical evaluation with proper ethical clearance. This 3D-printed hybrid microfluidic colorimetry-based creatinine detection and pH indicator platform can be beneficial in the healthcare sector due to the on-site testing capability, cost-effectiveness, ease of use, robustness, and instrument-free approach.

This study introduces the development of a photothermal-based microfluidic paper analytical device (PT-µPAD) integrated with near-field communication (NFC) technology and smartphone readout for enzyme-free glucose quantification in human samples. With the properties of gold nanoparticles (AuNPs) both as a nanozyme and as a photothermal substrate, there is no need for costly reagents like enzymes or a readout instrumentation for the selective and sensitive detection of glucose. In PT-µPADs, AuNPs are etched by hydrogen peroxide (H 2 O 2 ) generated from glucose catalysis. Photothermal detection from the plasmonic heating of these AuNPs when illuminated by a 533nm LED light source is achieved by inserting the PT-µPAD sensor into a portable NFC platform suitable for smartphone readout. Temperature variation is directly proportional to the glucose concentration. After optimization, we acquired a linear range between 5.0 and 20.0 µmol L -1 ( R 2 = 0.9967) and a limit of detection (LOD) of 25.0 nmol L -1 for glucose. Additionally, while our sensor does not utilize any enzyme, it is remarkably selective to glucose with no effects from interferences. Recovery studies in various human control samples indicated a range of 99.73-102.66% with the highest RSD of 3.53%, making it highly accurate and precise. Moreover, our method is more sensitive than other methods relying on conventional µPADs for glucose sensing. By integrating the potential benefits of microfluidics, nanomaterials as nanozymes, and NFC technology for wireless readout, our sensor demonstrates great promise as an accessible, affordable, and shelf-stable device for glucose quantification. Moreover, this concept can be extended to detect other molecules of interest as a point-of-care (POC) diagnostics device.

We reported a colorimetric paper-based device by integrating the modified acid RNA-cleaving DNAzymes (MaRCD-EC1) for highly sensitive (detection limit = 10 2 CFU mL -1 ), and rapid (within 30 min) detection of E. coli without amplification. This device exhibited a clinical sensitivity of 100% and a specificity of 100% in identifying E. coli -associated urinary tract infections (UTIs) using the clinical urine samples.

Safe, accurate, and reliable analysis of urinary biomarkers is clinically important for early detection and monitoring of the progression of chronic kidney disease (CKD), as it has become one of the world's most prevalent non-communicable diseases. However, current technologies for measuring urinary biomarkers are either time-consuming and limited to well-equipped hospitals or lack the necessary sensitivity for quantitative analysis and post a health risk to frontline practitioners. Here we report a robust paper-based dual functional biosensor, which is integrated with the clinical urine sampling vial, for the simultaneous and quantitative analysis of pH and glucose in urine. The pH sensor was fabricated by electrochemically depositing IrOx onto a paper substrate using optimised parameters, which enabled an ultrahigh sensitivity of 71.58 mV pH -1 . Glucose oxidase (GOx) was used in combination with an electrochemically deposited Prussian blue layer for the detection of glucose, and its performance was enhanced by gold nanoparticles (AuNPs), chitosan, and graphite composites, achieving a sensitivity of 1.5 μA mM -1 . This dual function biosensor was validated using clinical urine samples, where a correlation coefficient of 0.96 for pH and 0.98 for glucose detection was achieved with commercial methods as references. More importantly, the urine sampling vial was kept sealed throughout the sample-to-result process, which minimised the health risk to frontline practitioners and simplified the diagnostic procedures. This diagnostic platform, therefore, holds high promise as a rapid, accurate, safe, and user-friendly point-of-care (POC) technology for the analysis of urinary biomarkers in frontline clinical settings.

Plastic pollution at the nanoscale continues to pose adverse effects on environmental sustainability and human health. However, the detection of nanoplastics (NPLs) remains challenging due to limitations in methodology and instrumentation. Herein, a "green approach" for surface-enhanced Raman spectroscopy (SERS) was exploited to detect polystyrene nanospheres (PSNSs) in water, employing untreated filter paper and a simple syringe-filtration set-up. This SERS protocol not only enabled the filtration of nano-sized PSNSs, which are smaller than the pore size of the ordinary filter paper, but also offered SERS enhancement by utilizing quasi-spherical-shaped silver nanoparticles (AgNPs) as the SERS-active substrate. The filtering of NPLs was accomplished by adding an aggregating agent to the nanoparticle mixture, which caused the aggregation of NPLs and AgNPs, resulting in a larger cluster and more hot spots for SERS detection. The optimal aggregating agent and its concentration, as well as the volume ratio between the AgNPs and NPLs, were also optimized. This SERS method successfully detected and quantified PSNSs of various sizes (i.e., 100, 300, 460, 600, and 800 nm) down to a limit of detection (LOD) of about 0.31 μg mL−1. The method was also validated against the presence of several interferents (i.e., salts, sugars, amino acids, and surfactants) and was proven practical, as evidenced by the detection of 800nm PSNSs in drinking and tap water (LODs of 1.47 and 1.55 μg mL−1, respectively). [ABSTRACT FROM AUTHOR]

The accumulation of plastic packaging wastes in the natural environment highlights the significance of sustainable alternatives. Paper is widely used as a biodegradable packaging material, but poor mechanical strength, barrier properties, and water resistance limit its utility. Typical paper coating materials applied to overcome such drawbacks, such as polyethylene (PE) and ethylene vinyl alcohol (EVOH), are not desirable for sustainability due to environmental persistence. Here, we report a biodegradable, biocompatible, robust, and high-barrier paper coating strategy using boric acid-crosslinked poly(vinyl alcohol) (PVA). Various crosslinked-PVA solutions were prepared using boric acid (BA) and hydrochloric acid (HCl) as a crosslinker and an acid catalyst, respectively. The solutions were coated onto the Kraft paper (KP) through facile bar coating with epichlorohydrin (ECH) as a binder (henceforth referred to as coated papers). The coated papers (KP-P, KP-PB, KP-PBH) show remarkably improved oxygen (∼0.89 cc m−2 d−1) and water vapor (∼5.17 g m−2 d−1) barrier properties as well as tensile strength (∼53.0 MPa) that is retained in moist conditions. The coated papers were significantly mineralized into CO2 (59.2–81.6% over 111 d) in the simulated marine environment biodegradation test. Depolymerization of polymer chains and surface degradation of coated papers are evidenced via FT-IR and SEM, respectively. The microcosm test revealed that the intensive disintegration of the coated papers is synergistically driven by both biotic and abiotic factors (i.e., mechanical stress). Moreover, the in vitro biocompatibility tests employing human embryonic kidney and mouse embryonic fibroblast cells, and in vivo biocompatibility test with mice suggest that the coated papers are highly biocompatible. This work provides a promising strategy for paper packaging that enhances packaging performance without compromising environmental sustainability. [ABSTRACT FROM AUTHOR]

This report presents an investigation into the use of carbon paper electrodes prepared from chitosan-adhered graphene magnetite nanoparticles for the analysis of Cr(VI). The preparation and storage of carbon paper electrodes is a simple process, and these electrodes are easier to replace than electrodes modified by more conventional methods. The electrochemical detection of Cr(VI) using square wave adsorption cathodic dissolution voltammetry (SWAdCSV) with high selectivity and sensitivity, as well as the optimum conditions for the preparation of the electrodes and the electrode parameters affecting the SWAdCSV signal, were the main points of focus of the investigation. Cr(VI) was detected linearly in the range of 4-40 μg L-1 with a detection limit of 2.84 μg L-1. The electrode output precision, calculated as %RSD, was 7.16% (n = 6), and this was the measurement used for the detection of Cr(VI) in standard and test samples with recoveries between 89% and 114%. The results were consistent with those obtained using the standard UV-Vis spectrophotometric method with a paired t-test at 95% confidence level. [ABSTRACT FROM AUTHOR]

Non-enzymatic electrochemical blood glucose sensors often suffer from issues such as requiring an alkaline environment, limited monitoring range, and poor anti-interference properties. Carbon substrates have been demonstrated to improve the performance of non-enzymatic sensors, but complex and energy-consuming manufacturing processes restrict their use. Herein, a simple and green approach for the preparation of 3D porous Au/Au-Pt networks (PAAPNs) is proposed using tissue paper for recycling as the nanomaterial substrate to deposit Au-Pt bimetallic nanoparticles. The unique structure of the PAAPNs sensor allows for low-potential operation (-1.0 V) with a wide monitoring range (-0.25 to 36 mM) in a neutral environment. Moreover, the sensor exhibited excellent selectivity (<10% response of interference) even without the use of an anti-interference outer membrane. Further investigation using density functional theory (DFT) simulation revealed the synergistic effect between Au and Pt in promoting glucose oxidation. Overall, this work provides a simple and low-carbon footprint method for creating carbon substrates from tissue paper for recycling, offering new opportunities for fabricating novel value-added nanomaterials for medical sensing applications. [ABSTRACT FROM AUTHOR]

A new analytical method for chronic kidney disease (CKD) detection utilizing paper spray mass spectrometry (PS-MS) combined with machine learning is presented. The analytical protocol is rapid and simple, based on metabolic profile alterations in urine. Anonymized raw urine samples were deposited (10 μL each) onto pointed PS-MS sample strips. Without waiting for the sample to dry, 75 μL of acetonitrile and high voltage were applied to the strips, using high resolution mass spectrometry measurement (15 s per sample) with polarity switching to detect a wide range of metabolites. Random forest machine learning was used to classify the resulting data. The diagnostic performance for the potential diagnosis of CKD was evaluated for accuracy, sensitivity, and specificity, achieving results >96% for the training data and >91% for validation and test data sets. Metabolites selected by the classification model as up- or down-regulated in healthy or CKD samples were tentatively identified and in agreement with previously reported literature. The potential utilization of this approach to discriminate albuminuria categories (normo, micro, and macroalbuminuria) was also demonstrated. This study indicates that PS-MS combined with machine learning has the potential to be used as a rapid and simple diagnostic tool for CKD.

The first step in blood testing necessitates blood separation to obtain an adequate volume of plasma. Traditional centrifugation is bulky, expensive and electricity-powered, which is not suitable for micro-scale blood plasma separation in point-of-care testing (POCT) cases. Microfluidic paper-based plasma separation devices present a promising alternative for plasma separation in such occasions. However, they are limited in terms of plasma yield, which hinders analyte detection. Herein, we proposed a humidity-enhanced paper-based microfluidic plasma separation method to address this issue. Specifically, paper was first treated by blood-typing antibodies, then samples of whole blood were introduced into the prepared paper. After waiting for 5 min for RBC agglutination and plasma wicking under high humidity, micro-scale plasma separation from whole blood was achieved. As a result, an extremely high plasma yield of up to 60.1% could be separated from whole blood through using Xuan-paper. Meanwhile, the purity of plasma could reach 99.99%. Finally, this innovative approach was effortlessly integrated into distance-based glucose concentration detection, enabling rapid determination of blood glucose levels through naked-eye observation. Considering the simplicity and inexpensiveness of this method, we believe that this technology could be integrated to more paper-based microfluidic analytical devices for rapid and accurate detection of plasma analytes in POCT. [ABSTRACT FROM AUTHOR]

Paper-based microfluidics combined with potentiometric measurement has emerged as an attractive approach for detecting various chemical ionic moieties. Detection of heavy metal ions, using paper substrates as solution sampling and delivery systems remains challenging despite efforts to introduce several physico-chemical paper substrate modifications to stop adsorption of ions onto the paper substrates. This study quantitatively investigates the adsorption of heavy metal ions on the paper substrates during paper-based potentiometric measurements and explains the super-Nernstian response of potentiometric sensors through local depletion of heavy metal ions from the solution. Consequently, based on the investigated ion adsorption, a corrective potential protocol was established for the electrodes coupled with paper-based solution sampling by predicting interference free sensor response from paper-based measurement. Furthermore, the ion adsorption was also recorded for mixed metal ion solutions to understand competitive primary/interfering ions adsorption onto the paper substrates and establish corrective measures to predict interference free sensor response. In this method, no modifications of the paper substrates are necessary before actual potentiometric measurements. The proposed corrective protocol allows prediction of sensor response based on the paper-based solution sampling potentiometric measurement, providing a simple methodological approach based on correction of potential readout of the potentiometric sensor, thus completely resigning from the need of modifying paper substrate for measurements of heavy metal ions. [ABSTRACT FROM AUTHOR]

Serum contains rich elemental information, and the elemental analysis of the serum using laser-induced breakdown spectroscopy (LIBS) can help with the diagnosis and treatment of cancer. In this work, serum specimens from breast cancer patients were used as samples, and the elements Mg, Ca, and K were analyzed using LIBS. Silver nanoparticles (Ag NPs) were introduced to enhance spectral emission intensities, and this technique is known as nanoparticle-enhanced LIBS (NELIBS). An Ag NP-coated filter paper (Ag NP paper) substrate was prepared and was compared with silicon and aluminum substrates for NELIBS analysis. The Ag NP paper substrate showed lower spectral intensity variances and better elemental distribution uniformity due to the reduced coffee-ring effect compared with silicon and aluminum substrates. The enhanced effect of the Ag NP paper was optimized by adjusting serum volume and Ag NPs concentration. It was found that Mg, Ca, and K required different optimal conditions for spectral enhancement. The highest enhancement factors (EF) for Mg, Ca, and K were 1.85, 1.76, and 3.10, respectively. The electron temperature (Te) and electron number density (Ne) of NELIBS plasmas were measured using the Boltzmann plot and Stark broadening methods and compared with those of the normal LIBS plasmas. The Te and Ne of the NELIBS and normal LIBS samples were generally comparable with each other. Higher Ag NP concentrations led to lower Te values for NELIBS plasmas. [ABSTRACT FROM AUTHOR]

The demand for flexible pressure sensors with high performance is increasing with the growing wearable technology market. According to the developing requirement for green electronics, paper-based sensors, which are more environmentally friendly, have received more and more attention. However, the intrinsic mechanical properties of paper materials limit the sensing performance of paper-based sensors, such as restricted working range and response bandwidth. Herein, a rigid–soft hybrid design strategy is proposed to improve the sensing performance of paper-based pressure sensors, and bioinspired microstructures are introduced into the architecture of sensors for further improvement. As a result, the prepared paper-based pressure sensor has a faster response/recovery speed (<50 ms), a wide sensing range (1 MPa) and frequency response bandwidth (0.05–1000 Hz) and excellent cycling stability (5000 cycles). In addition, the paper-based pressure sensor is superhydrophobic with a water contact angle of 152.62°. Based on the excellent sensing performance and waterproofness, the paper-based pressure sensor can be used as a wearable device for detecting joint movements or gait of humans/robots in both air and underwater. In addition, it can be used to send communication signals, showing great potential for applications in future underwater rescue. [ABSTRACT FROM AUTHOR]

A simple, rapid chemical coating and patterning method was developed and optimized for paper-based substrates for use in paper spray mass spectrometry (PS-MS). A variety of chlorosilanes were explored for coating paper substrates, and their effectiveness in forming hydrophobic surfaces was characterized via contact angle goniometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Trichloromethylsilane was selected as the primary coating agent because of the short time required to produce a hydrophobic surface (contact angle > 130°), as well as the ease of patterning. Patterning was performed using 3D-printed masks and an oxygen/plasma cleaner. Optimal mask thickness and oxygen/plasma cleaning parameters were determined to produce channels varying from 0.5 to 2.5 mm in width. The effectiveness of the patterned substrates for PS-MS was determined via analysis of four antiretrovirals: emtricitabine, lamivudine, efavirenz, and dolutegravir. Calibration curves were made for each antiretroviral at varying channel widths, and the limits of detection and limits of quantification for each drug were determined. These results show that this patterning method results in an average 7.2-fold improvement in sensitivity and an average 190-fold improvement in limits of detection over uncoated paper substrates in a neat matrix. In a proof-of-concept experiment, calibration curves were generated for each antiretroviral in urine. A patterned paper substrate with a 2-mm channel resulted in an average 7.4-fold improvement in sensitivity and an average 18-fold improvement in limits of detection over uncoated paper substrates.

A simple and mild stimulus-responsive fluorescent supramolecular polymer network was constructed from a pillararene-based multi-functional monomer through multiple noncovalent interactions and used as a rewritable paper. [ABSTRACT FROM AUTHOR]

Multiple protocols have been reported to fabricate paper-based analytical devices (PADs). However, some of these techniques must be revised because of the instrumentation required. This paper describes a versatile and globally affordable method to fabricate PADs using office paper as a substrate and a laser printing technique to define hydrophobic barriers on paper surfaces. To demonstrate the feasibility of the alternatives proposed in this study, the fabrication of devices for three types of detection commonly associated with using PADs was demonstrated: colorimetric detection, electrochemical detection, and mass spectrometry associated with a paper-spray ionization (PSI-MS) technique. Besides that, an evaluation of the type of paper used and chemical modifications required on the substrate surface are also presented in this report. Overall, the developed protocol was suitable for using office paper as a substrate, and the laser printing technique as an efficient fabrication method when using this substrate is accessible at a resource-limited point-of-need. Target analytes were used as a proof of concept for these detection techniques. Colorimetric detection was carried out for acetaminophen, iron, nitrate, and nitrite with limits of detection of 0.04 μg, 4.5 mg mL−1, 2.7 μmol L−1, and 6.8 μmol L−1, respectively. A limit of detection of 0.048 fg mL−1 was obtained for the electrochemical analysis of prostate-specific antigen. Colorimetric and electrochemical devices revealed satisfactory performance when office paper with a grammage of 90 g m−2 was employed. Methyldopa analysis was also carried out using PSI-MS, which showed a good response in the same paper weight and behavior compared to chromatographic paper. [ABSTRACT FROM AUTHOR]

A new CdII-based luminescent metal–organic framework (LMOF) with the formula {[Cd(BIBT)(NDC)]·solvents}n (JXUST-32, BIBT = 4,7-bi(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole and H2NDC = 2,6-naphthalenedicarboxylic acid) was successfully synthesized by a solvothermal method. JXUST-32 shows a two-dimensional (4,4)-connected network and exhibits significant fluorescence red shift and slight enhancement for H2PO4− and CO32− sensing with detection limits of 0.11 and 0.12 μM, respectively. In addition, JXUST-32 has good thermal stability, chemical stability and recyclability. Significantly, JXUST-32 represents a fluorescence red-shift dual response MOF sensor for H2PO4− and CO32− detection and the analytes can be identified by the naked eye, aerosol jet printing filter paper, light-emitting diode beads and luminescent films. [ABSTRACT FROM AUTHOR]

As a kind of organic basic compound containing nitrogen, biogenic amine is released from food spoilage and considered as an indicator for monitoring food freshness. Herein, an excellent dual-emission ratiometric fluorescent sensor for eight kinds of biogenic amines was established via the facile mixing of pH-responsive carbon dots and Rhodamine B. The developed sensor shows a rapid response (10 s), low limit of detection (0.733–3.943 μM) and a wide linear range (0–150 μM). More importantly, a portable fluorescent filter paper was prepared by simple dispersing the filter paper in a solution mixture of carbon dots and Rhodamine B. The obtained fluorescent filter paper based sensor showed an obvious color change in the presence of biogenic amine vapor derived from shrimp and mushroom. The results revealed that this sensor could realize the on-site and visual detection of biogenic amines in real food samples, making it suitable for potential application in food safety monitoring. [ABSTRACT FROM AUTHOR]

Paper-based ratiometric fluorescence sensors are normally prepared using two or more types of fluorescent materials on a paper chip for simple, low-cost and fast detection. However, the choice of multi-step and one-step modifications on the paper chip affects the analytical performance. Herein, a novel paper-based dual-emission ratiometric fluorescence sensor was designed for the selective detection of tetracycline (TC). Carbon dots (CDs) modified with Eu3+ were combined with a sealed paper-based microfluidic chip by two methods: one-step grafting of CDs-Eu3+ on paper and step-by-step grafting of CDs and Eu3+ on paper. The analytical performance was studied and optimized respectively. The red fluorescence of Eu3+ at 450 nm is enhanced and the blue fluorescence of CDs at 617 nm is quenched by energy transfer in the presence of TC. Under optimal conditions, TC is selectively determined in the linear range from 0.1 μM to 100 μM with a detection limit of 0.03 μM by the step-by-step grafting method. In addition, the sealed paper chip could effectively prevent pollution and volatilization from the reagent. This technique has been used to analyze TC in seafood aquaculture water with satisfactory results. [ABSTRACT FROM AUTHOR]

Conventional affinity-based colorimetric enzyme-linked immunosorbent assay (ELISA) is one of the most widely used methods for the detection of biomarkers. However, rapid point-of-care (POC) detection of multiple cancer biomarkers by conventional ELISA is limited by long incubation time, large reagent volume, and costly instrumentation along with low sensitivity due to the nature of colorimetric methods. Herein, we have developed a reusable and cost-effective paper-in-polymer-pond (PiPP) hybrid microfluidic microplate for ultrasensitive and high-throughput multiplexed detection of disease biomarkers within an hour without using specialized instruments. A piece of pre-patterned chromatography paper placed in the PMMA polymer pond facilitates rapid protein immobilization to avoid intricate surface modifications of polymer and can be changed with a fresh paper layer to reuse the device. Reagents can be simply delivered from the top PMMA layer to multiple microwells in the middle PMMA layer via flow-through microwells, thereby increasing the efficiency of washing and avoiding repeated manual pipetting or costly robots. Quantitative colorimetric analysis was achieved by calculating the brightness of images scanned by an office scanner or a smartphone camera. Sandwich-type immunoassay was performed in the PiPP hybrid device after the optimization of multiple assay conditions. Limits of detection of 0.32 ng mL -1 for carcinoembryonic antigen (CEA) and 0.20 ng mL -1 for prostate-specific antigen (PSA) were obtained, which were about 10-fold better than those of commercial ELISA kits. We envisage that this simple but versatile hybrid device can have broad applications in various bioassays in resource-limited settings.

The development of novel rare earth fluorescent materials and the exploration of their applications have consistently been focal points of research in the fields of materials science and chemistry. In this work, a novel rare earth composite material with good photo-fluorescence properties and self-supporting has been prepared via a simple ultrasonic solvent reaction method. Initially, the Phen moieties is immobilized onto the surface of a self-supporting fiberglass paper using ICPTES, followed by the coordination of Eu(TTA) 3 moieties with Phen moieties through a convenient ultrasonic solvent reaction. The resulting GF-Phen-Eu(TTA) 3 has been characterized using FTIR, UV-Vis DRS, fluorescence measurements, and so on. The results indicate that the composite material exhibits strong fluorescent emission and presents a vivid red color under ultraviolet light. Further research has shown that the fluorescence of GF-Phen-Eu(TTA) 3 strips demonstrated a pronounced quenching effect in response to some transition metal ions (1 mM). Hence, the rare earth composite materials presented here can be utilized not only for the production of optical materials, but also for the development of fluorescence sensing strips., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

Isothermal nucleic acid amplification tests (NAATs) are a vital tool for point-of-care (POC) diagnostics. These assays are well-suited for rapid, low-cost POC diagnostics for infectious diseases compared to traditional PCR tests conducted in central laboratories. There has been significant development of POC NAATs using paper-based diagnostic devices because they provide an affordable, user-friendly, and easy to store format; however, the difficulties in integrating separate liquid components, resuspending dried reagents, and achieving a low limit of detection hinder their use in commercial applications. Several studies report low assay efficiencies, poor detection output, and poorer limits of detection in porous membranes compared to traditional tube-based protocols. Recombinase polymerase amplification is a rapid, isothermal NAAT that is highly suited for POC applications, but requires viscous reaction conditions that has poor performance when amplifying in a porous paper membrane. In this work, we show that we can dramatically improve the performance of membrane-based recombinase polymerase amplification (RPA) of HIV-1 DNA and viral RNA by employing a coin cell-based vibration mixing platform. We achieve a limit of detection of 12 copies of DNA per reaction, nearly 50% reduction in time to threshold (from ∼10 minutes to ∼5 minutes), and an overall fluorescence output increase up to 16-fold when compared to unmixed experiments. This active mixing strategy enables reactions where the target and reaction cofactors are isolated from each other prior to the reaction. We also demonstrate amplification using a low-cost vibration motor for both temperature control and mixing, without the requirement of any additional heating components.

Paper-based sensors or paper-based analytical devices (PADs) have recently emerged as the cost-efficient, and portable, on-site detection tools for various biological and environmental analytes. However, paper-based sensors often suffer from poor selectivity. Here, a single-step paper-based flexible sensor platform has been developed for the on-site detection of paraquat (PQ) pesticide in real samples, utilizing chitosan and citrate-capped silver nanoparticles integrated with a flexible paper. The nanocomposite paper film was thoroughly characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The composite paper platform demonstrated a color change with a reaction time within a few minutes (6-7 min) in the presence of PQ pesticide. The trace level PQ pesticide has been detected with a limit of detection (LOD) of 10 μM and a linear range (LR) of 10-100 μM. The sensor shows 3× more selective signal towards PQ pesticide compared to other similar pesticides. The relative standard deviation (RSD) was found to be 5% for repeatability, 4% for reproducibility, 2% for interference, and 3.5% for real sample analysis, indicating high precision sensing and within the WHO limit of RSD (20%). The present work will open up new avenues for the advancements in flexible paper sensors; cost-effective, portable, on-site sensors, and sustainable device development., Competing Interests: The authors have no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Bacillus cereus is a foodborne opportunistic pathogen commonly found in humans and animals. It produces various toxins, causing frequent food safety incidents. Therefore, establishing a fast and accurate method for detecting B. cereus enterotoxin is crucial for disease diagnosis and food safety. In this study, Haemolysin BL comprising Hbl B and L2 was obtained from a prokaryotic expression system and then used to immunize mice for antibody preparation. Paired antibodies 2A10-5C7 against Hbl B and 1E2-10A4 against Hbl L2 were screened using the chessboard method and then used to construct a double-antibody sandwich detection method and a lateral flow immunochromatographic assay (LFIA) to quantify the concentrations of Hbl B and L2 in PBS and milk. The limits of detection for Hbl B and L2 in milk were 0.74 ng mL -1 and 1 ng mL -1 with detection ranges of 1.48-645.5 ng mL -1 and 2.33-391.5 ng mL -1 . The spiked recoveries ranged from 82.2% to 105.67% and there was no cross-reactivity with common microbial toxins. The established LFIA was low in cost and rapid and was comparable with commercially available detection kits for food samples.

Gold nanoclusters (AuNCs) are a type of rising-star fluorescence nanomaterials, but their properties and applications are hindered by the multi-step synthesis and purification routes, as well as the lack of desired supporting substrates. To enhance optical performance and working efficiency, the synthesis and applications of AuNCs are suggested to be merged with emerging substrates. Herein, glutathione-modified hydrophilic rice papers are incubated in chloroauric acid aqueous solutions, and the oxidation-reduction reaction between glutathione and Au ions enables the in situ formation of fluorescent AuNCs on the solid fibres of rice papers. The in situ growth of fluorescent AuNCs on rice papers resulted in eye-catching fluorescence tracks, similar to traditional Chinese conventional calligraphy; thus, this fluoresence calligraphy is defined in this work. The entire process, including synthesis and signal responses, is extremely simple, rapid, and repeatable. Moreover, the diversity of additive chemical reagents in the studied rice papers resulted in responsive fluorescence calligraphy, and the as-synthesized AuNC materials exhibited high reliability and optical stability. Significantly, with the integration of synchronous formation and application of Au nanoclusters on hydrophilic paper substrates, high-performance logical gates and information encryption systems were constructed, remarkably facilitating the progress of molecular sensing and important information transmission.

Lumpy skin disease (LSD) is a contagious viral disease caused by the Lumpy Skin Disease virus (LSDV), a member of the Capripoxviridae family. Traditional LSDV diagnostic procedures proved to have challenges in terms of cross reactivity as well as limited sensitivity and specificity. Herein, we combined molecularly imprinted polymers (MIPs) and quantum dots (QDs) technology to develop a paper-based turn on fluorescence sensor for rapid, sensitive and selective detection of LSDV. Under optimal conditions, the sensor showed linear enhancement in fluorescence intensity with the increase of LSDV concentration and exhibited a detection limit of 10 1 log 10 TCID50 per ml. It also presented high specificity towards LSDV compared to other viruses viz sheep pox virus (SPV). Furthermore, the proposed sensor was successfully tested with spiked and real LSDV samples, proving its potential to serve as a sensitive selective sensor for LSDV diagnosis. Based on our knowledge, this is the first record of a paper-based diagnostic sensor for LSDV utilizing a CQDs-MIPs turn-on mechanism., Competing Interests: Authors declared no conflict of interest., (This journal is © The Royal Society of Chemistry.)

We investigate the adsorption behavior of polar and nonpolar molecules on carbon nanotube interfaces through computational simulations. Gaussian 16 was utilized to calculate the total energy of each possible molecular structure and analyze the adsorption mechanisms in stacked and inline configurations. The study reveals that nonpolar molecules favor stacked adsorption on two graphene interfaces, while polar molecules prefer inline adsorption. The findings suggest that inline adsorption of polar molecules results in minimal changes to the local dielectric constant, which may explain the absence of multi-step adsorption isotherms. The research examines the stability and energetics of molecular adsorption on graphene layers simulating CNT interfaces. Different types of molecules (polar and nonpolar) exhibit distinct adsorption behaviors, with nonpolar molecules aligning with the IUPAC type VI isotherm model and polar molecules following the Langmuir isotherm model (IUPAC type I). This study provides insight into how molecules are likely to adsorb on CNT surfaces and the impact on the local dielectric constant. This understanding has implications for the design and optimization of CNT-based sensors, particularly in detecting organic solvents and gases in various environments., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Contact lenses offer a simple, cost-effective, and non-invasive method for in situ real-time analysis of various biomarkers. Electro-chemical sensors are integrated into contact lenses for analysis of various biomarkers. However, they suffer from rigid electronic components and connections, leading to eye irritation and biomarker concentration deviation. Here, a flexible and microfluidic integrated paper-based contact lens for colorimetric analysis of glucose was implemented. Facilitating a three-dimensional (3D) printer for lens fabrication eliminates cumbersome cleanroom processes and provides a simple, batch compatible process. Due to the capillary force of the filter paper, the sample was routed to detection chambers inside microchannels, and it allowed further colorimetric detection. The paper-embedded microfluidic contact lens successfully detects glucose down to 2 mM within ∼10 s. The small dimension of the microfluidic system enables detection of glucose levels as low as 5 μl. The results show the potential of the presented approach to analyze glucose concentration in a rapid manner. It is demonstrated that the fabricated contact lens can successfully detect glucose levels of diabetic patients., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Pancreatitis is a life-threatening inflammatory disease of the pancreas. In 2019, 34.8 out of 100 000 people suffered from acute pancreatitis globally. In humans, the level of α-amylase increases three times the normal value during pancreatitis. α-Amylase is an enzyme that hydrolyses α-1,4 glycosidic bonds of starch. In this study, we investigated a novel distance-based sensing method. We exploited the existing starch triiodide method, where the blue colour of starch-triiodide fades away and becomes colourless when α-amylase breaks the starch chain at the α-1-4 glycosidic bond. A hydrophilic channel was made on paper using a simple laser printer to create hydrophobic barriers. This channel was impregnated with starch triiodide, where α-amylase can turn it colourless. This distance covered by the change in colour is directly proportional to the concentration of α-amylase in a sample. Simulated samples with different concentrations of porcine α-amylase and pancreatin were used for testing using the developed paper-based chemometer device. The paper-based chemometer device was also tested with artificial blood serum with different concentrations of α-amylase. The R 2 of this device was found to be 0.9905, and the accuracy of the device when compared with a 2-chloro-4-nitrophenyl-α-d-maltotrioside method was found to be 95.54% with a sensitivity of 0.131 U L -1 . Correlation test also showed that the paper-based chemometer device for α-amylase can be used as a testing device for artificial blood serum. This is a preliminary investigation that shows promising results. The chemometer devices stored in air-tight packets at 4-8 °C in a refrigerator did not lose the colour intensity until day 90 and retained an accuracy of 94.5%. However, the device needs to be evaluated in clinical settings prior to using it for measuring α-amylase in patients.-1 . Correlation test also showed that the paper-based chemometer device for α-amylase can be used as a testing device for artificial blood serum. This is a preliminary investigation that shows promising results. The chemometer devices stored in air-tight packets at 4-8 °C in a refrigerator did not lose the colour intensity until day 90 and retained an accuracy of 94.5%. However, the device needs to be evaluated in clinical settings prior to using it for measuring α-amylase in patients., Competing Interests: There is no conflict of interest., (This journal is © The Royal Society of Chemistry.)

We have developed an easily scalable chromogenic probe for the dual-mode sensing of Spilosoma obliqua Nuclear polyhedrosis viruses (SpobNPV) in aqueous media. The mechanistic investigations establish that the imidazole-mediated hydrolysis of acyl ester linkage in which water (general base) acts as a nucleophile induces a pronounced change in the emission colour from blue to cyan. To the best of our knowledge, this is the first attempt at quantifying OBs of SpobNPV using a small molecule-based optical probe with a detection limit of 2.305 × 10 3 OBs mL -1 . The rate of ester hydrolysis was dependent on both substrate and OBs concentration. Due to the naked eye response, paper strips were also developed for the rapid and onsite detection of SpobNPV. The operation procedure is straightforward and does not involve additional sample preparation steps. This makes the present protocol suitable for daily use. Interestingly, the present protocol is also quite efficient in estimating SpobNPV, even in several agricultural crop samples (for at least 15 crops). Such findings will add a new dimension to better managing Spilosoma obliqua and minimizing the extent of crop loss.

The United Nations estimates that by 2030, agricultural production must increase by 70% to meet food demand. Precision agriculture (PA) optimizes production through efficient resource use, with soil fertility being crucial for nutrient supply. Traditional nutrient quantification methods are costly and time-consuming. This study introduces a rapid (15 min), user-friendly, paper-based platform for determining four essential macronutrients-nitrate, magnesium, calcium, and ammonium-using colorimetric methods and a smartphone for data reading and storage. The sensor effectively detects typical soil nutrient concentrations, showing strong linearity and adequate detection limits. For nitrate, the RGB method resulted in an R 2 of 0.992, a detection range of 0.5 to 10.0 mmol L -1 , and an LOD of 0.299 mmol L -1 . Calcium quantification using grayscale displayed an R 2 of 0.993, a detection range of 2.0 to 6.0 mmol L -1 , and an LOD of 0.595 mmol L -1 . Magnesium was best quantified using the hue color space, with an R 2 of 0.999, a detection range of 1.0 to 6.0 mmol L -1 , and an LOD of 0.144 mmol L -1 . Similarly, ammonium detection using the hue color space had an R 2 of 0.988, a range of 0.5 to 2.5 mmol L -1 , and an LOD of 0.170 mmol L -1 . This device enhances soil fertility assessment accessibility, supporting PA implementation and higher food production., Competing Interests: The authors have no competing interests to declare that are relevant to the content of this article., (This journal is © The Royal Society of Chemistry.)

In this work, we report on five novel coordination polymers (CPs) based on the linkage of the [Cd(6apic) 2 ] building block [where 6apic = 6-aminopicolinate] by different bipyridine-type organic spacers, forming different coordination compounds with the following formulae: [Cd(μ-6apic) 2 ] n (1), {[Cd(6apic) 2 (μ-bipy)]·H 2 O} n (2), {[Cd(6apic) 2 (μ-bpe)]·2H 2 O} n (3), [Cd(6apic)(μ-6apic)(μ-bpa) 0.5 ] n (4) and {[Cd 2 (6apic) 4 (μ-tmbp)]·7H 2 O} n (5) [where bipy = 4,4'-bipyridine, bpe = 1,2-di(4-pyridyl)ethylene, bpa = 1,2-di(4-pyridyl)ethane (bpa) and tmbp = 1,3-di(4-pyridyl)propane]. Most of the synthesized compounds form infinite metal-organic rods through the linkage of the building block by the bipyridine-type linker, except in the case of compound 4 whose assembly forms a densely packed 3D architecture. All compounds were fully characterized and their photoluminescence properties were studied experimentally and computationally through density functional theory (DFT) calculations. All compounds display, upon UV excitation, a similar blue emission of variable intensity depending on the linker employed for the connection of the building units, among which compound 2 deserves to be highlighted for its room temperature phosphorescence (RTP) with an emission lifetime of 32 ms that extends to 79 ms at low temperature. These good photoluminescence properties, in addition to its stability in water over a wide pH range (between 2 and 10), motivated us to study compound 2 as a sensor for the detection of metal ions in water, and it showed high sensitivity to Fe 3+ through a fluorescence turn-off mechanism and an unspecific turn-on response to Zn 2+ . Furthermore, the compound is processed as a paper-based analytical device (PAD) in which the phosphorescence emission is preserved, improving the sensing capacity toward Fe 3+ ions.

The correct interpretation of the result from a point-of-care device is crucial for an accurate and rapid diagnosis to guide subsequent treatment. Lateral flow tests (LFTs) use a well-established format that was designed to simplify the user experience. However, the LFT device architecture is inherently limited to detecting analytes that can be captured by molecular recognition. Microfluidic paper-based analytical devices (μPADs), like LFTs, have the potential to be used in diagnostic applications at the point of care. However, μPADs have not gained significant traction outside of academic laboratories, in part, because they have often demonstrated a lack of homogeneous shape or color in signal outputs, which consequently can lead to inaccurate interpretation of results by users. Here, we demonstrate a new class of μPADs that form colorimetric signals at the interfaces of converging liquid fronts ( i.e. , lines) to control where colorimetric signals are formed without relying on capture techniques. We demonstrate our approach by developing assays for three classes of analytes-an ion, an enzyme, and a small molecule-to measure using iron(III), acetylcholinesterase, and lactate, respectively. Additionally, we show these devices have the potential to support multiplexed assays by generating multiple lines in a common readout zone. These results highlight the ability of this new paper-based device architecture to aid the interpretation of assays that create soluble products by using flow to constrain those colorimetric products in a familiar, line-format output.

Lab-on-a-paper-based devices are promising alternatives to the existing arduous techniques for point-of-need monitoring. The present work reports an instant and facile method to produce a microfluidic paper-based analytical device (μPAD). The fabricated μPAD has been used to detect hypochlorite (OCl - ) by incorporating newly synthesized chromo-fluorogenic ratiometric probes 1 and 2 into the sample reception zone. The probes showed high selectivity and fast response (<10 s) toward OCl - with an excellent linear relationship in the concentration range of 0-100 μM. The concentration-dependent fluorometric change driven by the reaction of 1@μPAD with OCl - has been monitored using gel-doc imaging systems, which is unprecedented. Digitizing the intensity of the colour solution with different mathematical models of colour has developed a straightforward method for monitoring OCl - without any interference from its competitors. 1@μPAD can detect OCl - at ∼10 times lower than the WHO recommended limit. The detection limit of 1@μPAD via a digital camera-based fluorescence technique was found to be better over digital camera-based cuvette assays. Therefore, 1@μPAD has been successfully utilized to monitor OCl - in actual environmental water samples with portability, ease of use, and sensitivity. The analytical RSD was found to be ≤3% based on fluorimetric detection using 1@μPAD. The chemodosimetric reaction between OCl - and the probe was evidenced by UV-vis and fluorescence spectroscopy, 1 H NMR, and ESI-MS. The rapid response time, biocompatibility, low cytotoxicity, 100% aqueous solubility, ratiometric feature, and exclusive OCl - selectivity over other competitive ROS/RNS successfully lead to the application of the probes for bioimaging of exogenous as well as endogenous OCl - in normal cells (HEK293) and cancerous cells (HeLa).

Developing new forms of flexible zinc–air (Zn–air) batteries is crucial to economic growth. Nevertheless, the absence of an oxygen evolution reaction catalyst with high catalytic efficiency and low-cost causes instability of Zn–air battery cycling and economic unviability, respectively. In this paper, a leaf-like N-doped carbon structure with CoS2 nanoparticles self-supported on carbon fiber paper (CoS2-CZ@CFP) was developed as an air electrode for Zn–air batteries, which not only uses nonprecious metal elements, but also has a self-supporting configuration, enhancing the contact between the catalyst and electrode while facilitating the transfer of electrons. Sulfur as the source gas was introduced into Co-doped metal–organic skeletons (Co-ZIFs) anchored on carbon fiber paper (CFP) for in situ vulcanizing transition metal Co, which successfully ensures the uniform distribution of sulfide particles in the carbon matrix, hence enriching active catalyst sites. The CoS2-CZ@CFP demonstrated an overpotential of 1.611 V at J = 50 mA cm−2, superior to RuO2@CFP (1.814 V). A Zn–air battery fabricated using the synthesized CoS2-CZ@CFP exhibited an extended life cycle of 117 h. This research paves the way for a novel method of designing self-supporting configurations of sulfides and carbon matrix composites as promising air electrodes applicable to Zn–air batteries. [ABSTRACT FROM AUTHOR]

Selective enrichment of La(III) by green material as an industrial raw material is of great research interest. In this study, the selective interaction between P and La(III) was utilized, and waste paper (WP) modified with phytic acid (PA) was used to adsorb La(III) from water using a simple one-pot method. The adsorption capacity was 237.23 mg g−1 (30 °C, pH = 5, initial concentration of 200 mg L−1). The equilibrium isotherm fitted the Langmuir isotherm model well. The adsorption equilibrium was reached after 15 min. The adsorption kinetics followed the pseudo-second-order kinetic model, indicating that the adsorption mechanism of the material towards La(III) is single-layer chemisorption. It selectively adsorbed La(III) from four coexisting substances (Pb, Ni, Cu, and Co). After six cycles, the adsorption efficiency of the adsorbent material remained at 60%. [ABSTRACT FROM AUTHOR]

In this work, we report on five novel coordination polymers (CPs) based on the linkage of the [Cd(6apic)2] building block [where 6apic = 6-aminopicolinate] by different bipyridine-type organic spacers, forming different coordination compounds with the following formulae: [Cd(μ-6apic)2]n (1), {[Cd(6apic)2(μ-bipy)]·H2O}n (2), {[Cd(6apic)2(μ-bpe)]·2H2O}n (3), [Cd(6apic)(μ-6apic)(μ-bpa)0.5]n (4) and {[Cd2(6apic)4(μ-tmbp)]·7H2O}n (5) [where bipy = 4,4′-bipyridine, bpe = 1,2-di(4-pyridyl)ethylene, bpa = 1,2-di(4-pyridyl)ethane (bpa) and tmbp = 1,3-di(4-pyridyl)propane]. Most of the synthesized compounds form infinite metal–organic rods through the linkage of the building block by the bipyridine-type linker, except in the case of compound 4 whose assembly forms a densely packed 3D architecture. All compounds were fully characterized and their photoluminescence properties were studied experimentally and computationally through density functional theory (DFT) calculations. All compounds display, upon UV excitation, a similar blue emission of variable intensity depending on the linker employed for the connection of the building units, among which compound 2 deserves to be highlighted for its room temperature phosphorescence (RTP) with an emission lifetime of 32 ms that extends to 79 ms at low temperature. These good photoluminescence properties, in addition to its stability in water over a wide pH range (between 2 and 10), motivated us to study compound 2 as a sensor for the detection of metal ions in water, and it showed high sensitivity to Fe3+ through a fluorescence turn-off mechanism and an unspecific turn-on response to Zn2+. Furthermore, the compound is processed as a paper-based analytical device (PAD) in which the phosphorescence emission is preserved, improving the sensing capacity toward Fe3+ ions. [ABSTRACT FROM AUTHOR]