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Rapid, simple, and sensitive analysis of relevant proteins is crucial in many research areas, such as clinical diagnosis and biomarker detection. In particular, clinical data on cancer biomarkers show great promise in forming reliable predictions for early cancer diagnostics, although the current analytical systems are difficult to implement in regions of limited recourses. Paper-based biosensors, in particular, have recently received great interest because they meet the criteria for point-of-care (PoC) devices; the main drawbacks with these devices are the low sensitivity and efficiency in performing quantitative measurements. In this work, we design a low-cost paper-based nanosensor through plasmonic calligraphy by directly drawing individual plasmonic lines on filter paper using a ballpoint pen filled with gold nanorods (AuNR) as the colloidal ink. The plasmonic arrays were further successively coated with negatively and positively charged polyelectrolyte layers employed as dielectric spacers to promote the enhancement of the emission of carboxyl-functionalized quantum dots (QD)—previously conjugated with specific antibodies—for indirect detection of the carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5). The efficiency, sensitivity, as well as the specificity of our portable nanosensor were validated by recording the luminescence of the QD@Ab complex when different concentrations of CEACAM5 were added dropwise onto the calligraphed plasmonic arrays. [ABSTRACT FROM AUTHOR]

The utility of strikingly simple and cheap optoelectronic detectors operating according to a Paired-Emitter-Detector-Diode (PEDD) principle for microfluidic paper-based analytical devices (μPAD) has been experimentally confirmed. The prototypes of these compact detectors have been made of only two customary light emitting diodes without any additional optical parts like lens, filters, fibers etc. Moreover, for their operation economic and portable equipment is required (low-power circuit and ordinary voltmeter). Photometric and fluorometric PEDDs for paper devices are developed. In both cases the possibility of their applicability in transmittance and reflectance modes of measurements are presented. In these investigations as model analytes some coloured and fluorescence substances have been handled, but the utility of several developed systems for real chemical analysis has also been demonstrated. The results of photometric determination of hemoglobin in human blood, as well as fluorometric determination of quinine in tonics and calcium ions in mineral waters using various PEDD-μPAD systems have been shown. [ABSTRACT FROM AUTHOR]

There is growing interest in developing printable paper sensors to enable rapid testing of analytes for environmental, food safety, and clinical applications. A major challenge is to find suitable bioinks that are amenable to high-speed printing and remain functional after printing. We report on a simple and effective approach wherein an aqueous ink composed of megadalton-sized tandem repeating structure-switching DNA aptamers (concatemeric aptamers) is used to rapidly create patterned paper sensors on filter paper by inkjet printing. These concatemeric aptamer reporters remain immobilized at the point of printing through strong adsorption but retain sufficient segmental mobility to undergo structure switching and fluorescence signaling to provide both qualitative and quantitative detection of small molecules and protein targets. The convenience of inkjet printing allows for the patterning of internally referenced sensors with multiplexed detection, and provides a generic platform for on-demand printing of sensors even in remote locations. [ABSTRACT FROM AUTHOR]

Abstract: Acidity (pH) is one of the most important factors for the stability of paper arts. In this study, a new fluorescent nanosensor was developed for measurement surface pH of paper. The nanosensor is based on the chitosan-modified silica nanoparticles, where Ru(bpy)3 2+ (bpy=2,2′-bipyridyl) was doped in the nanoparticles as reference dye and pH sensitive fluorescein isothiocyanate (FITC) were used as pH indicator. The nanocomposite was prepared by the modified reverse microemulsion method, and characterized by TEM, XPS and Uv–vis spectra. The pH nanosensor showed the linear dynamic range from 5.5 to 8.0. The dynamic performances of the nanosensor on the paper fiber showed the nanosensor was suitable for sensing in-situ surface pH of paper fiber because it could actively infiltrate into the surface of paper fiber. We demonstrated one practical application of the nanosensor for detection of surface pH in the precious art sample by integrating our nanosensor into the paper fiber. Simply washing by water, the nanosensor could be easily removed from the measured precious art sample without any damage after measurement. Taken together, this work established a modular approach to pH nanosensor design for detection of surface pH in precious art sample. Chitosan-modified nanosensor could also extend to detect pH of specific analytic samples. [Copyright &y& Elsevier]

The analysis of Fluorescence Recovery After Photobleaching (FRAP) experiments involves mathematical modeling of the fluorescence recovery process. An important feature of FRAP experiments that tends to be ignored in the modeling is that there can be a significant loss of fluorescence due to bleaching during image capture. In this paper, we explicitly include the effects of bleaching during image capture in the model for the recovery process, instead of correcting for the effects of bleaching using reference measurements. Using experimental examples, we demonstrate the usefulness of such an approach in FRAP analysis. [ABSTRACT FROM AUTHOR]

Evaluation of paper brightness in multipage documents is a practice of forensic document examiners when there is a question of a page insertion or substitution. This article demonstrates that occasional errors occur in the manufacturing process that affects the consistency of paper brightness. The inconsistency of paper brightness may therefore influence conclusions reached in authenticating documents. Reams of multipurpose paper, from 21 manufacturers, were examined. When assessing the individual pages of each package with an ultraviolet light, approximately 30% of the reams revealed differences in paper brightness. A study of the paper-manufacturing process was conducted to determine where variations originate. It is concluded that brightness differences occur when one incompatible roll of paper is mistakenly placed with others used for one production run. It was also determined that brightness variations (when present) are patterned throughout individual reams. When the authenticity of a document is in question, consideration of these findings is essential to assure an accurate assessment. [ABSTRACT FROM AUTHOR]

Abstract: Latent fingermarks were deposited onto white office paper samples containing writing or printing from several media (for example, ballpoint pens and laser printers). Fingermarks were deposited both before and after writing/printing. The marks were then treated with appropriate latent fingermark development techniques. Once treated, they were examined with standard techniques applied in document examination (filtered light analysis, electrostatic detection device and Raman spectroscopy) to determine the sequence of application. The results suggested that the sequence of laser printing and latent marks could be determined via electrostatic detection device examination of undeveloped and Ninhydrin developed samples. [Copyright &y& Elsevier]

Although the ability to develop latent fingerprints on paper using heat alone has been noted previously, it has been considered impractical for casework and inferior to other techniques. Here a new refinement of the technique is demonstrated for the high quality development of latent fingerprints on porous surfaces such as paper. Fingerprints deposited on various papers were developed by exposing them to hot air with a temperature in the vicinity of 300°C, for periods of c. 10–20 sec. Several different heating methods were tested. The novel observation was made that after shorter heating times, fluorescent prints could be observed. These became visible after longer heating times, as noted by earlier workers, but with greatly improved contrast compared with their results. Prints from various donors (and aged prints) were developed with excellent ridge contrast. Direct heating methods (such as with a hot plate or press) produced inferior results. The refined technique, which is simple, safe and inexpensive compared with conventional methods, has great potential for use in forensic laboratories. [ABSTRACT FROM AUTHOR]

AbstractSamples of two historical papers from the late 17th and early 18th centuries were irradiated with a 350-nm ?maxlight source. Atomic force microscopy examination of untreated samples of these laid paper sheets revealed notable surface inhomogeneity. Diffuse brightness values show that irradiation resulted in an initial decrease followed by a rapid increase in brightness with increasing irradiation time from 0.5 to 28 h. The bleaching effect then slowed, following a logarithmic path that did not plateau within 197 h of irradiation time. Irradiated sheets stored for 3 months exhibited brightness reversion of 7%. Fluorescence also decreased with irradiation time if excitation wavelengths of 320, 350, and 400 nm were applied for samples exposed to narrow-band irradiation at 350 nm. The fold endurance decreased by 34–72% after 197 h of irradiation. Changes in tear and tensile values were less dramatic. The Z-direction ultrasonic velocity decreased after 197 h of irradiation; however, the ultrasonic conductivity partially recovered during 9 months of storage. [ABSTRACT FROM AUTHOR]

After initial tests carried out on 20 stained paper samples from different centuries, we have devised a non-destructive method for taking samples from foxed areas of ancient maps. The stains were examined in normal light (NL) and then with fluorescence; we then checked whether fungal colonies were not developing in areas that did not respond to electronic excitation. Samples were taken using gauze–cotton swabs from fluorescent areas only. We found that fungi did develop, in the areas of the paper samples that were not clearly visible (NL) but fluorescent, when they were placed inside humidity chambers. It was confirmed that there is a correlation between the thermo-hygrometric parameters and the place of preservation and a relationship between the environment and the fungal species. We found cellulosolithic fungi and bacteria. We recommend early identification of “discolouring” with fluorescent methods in order to arrange suitable thermo-hygrometric conditions for preventing development of the infection. [Copyright &y& Elsevier]

Foxing spots appear on the paper as stains of reddish-brown, brown or yellowish color, generally of small dimensions, with sharp or irregular edges, most of which, if excited with UV light, show fluorescence. The formation mechanisms of foxed areas have been studied since 1935, however, despite more recent intensive research there are still no conclusive results. Some authors found evidence of bacterial or fungal growth in some foxed areas sometimes associated with the presence of iron. We decided to focus our attention on the influence of the different iron valence in the formation of stains in the paper. For this reason we artificially induced the formation of foxing by adding to the paper small, known quantities of iron (III) and iron (II) ions. We prepared aqueous solutions of ferric chloride and ferrous sulfate at three different concentrations and we always used the same quantity of each solution (5 μl) to obtain a foxing stain. Part of the paper samples was artificially aged in a climatic chamber at 80 °C, 65% relative humidity for 15 days and part was submitted to aging for the same period at ambient temperatures under UV light at 240 nm. All papers were then analyzed for stain diameter, chromaticity coordinates, fluorescence under UV illumination, water content in the paper and in the spots, carbonyl content and then examined with infrared spectroscopy, X-ray fluorescence spectrometry and laser induced breakdown spectroscopy. Infrared spectra were collected in transmittance from potassium bromide pellets or directly in reflectance under microscope; X-ray fluorescence analysis were carried out using an X-ray microbeam (350 μm beam spot; W X-ray tube) and LIBS analysis with Nd:YAG laser coupled with a Czerny-Turner spectrometer. As a result it is stated that the foxing phenomenon is related to a strong oxidation of the cellulose chain. Concerning the color coordinates there are no great differences between samples treated with iron (III) and iron (II). Carbonyl content, on the contrary, varies for the two sets of samples, especially in relation with the kind of aging. μ-XRF and LIBS measurements show a relationship between iron valence and calcium ion displacement in the foxed areas. [Copyright &y& Elsevier]

Paper-based diagnostic assay is quite popular in point-of-care testing (POCT). In this work, we reported a series of hybrid fluorophores based on fluorescein derivatives and investigated their fluorescent properties in detail. To extend the practical application of these hybrid fluorophores, we further constructed the corresponding probes (FN1-FN4) for Cu2+ detection. In comparison with the other three probes, FN4 showed high selectivity and sensitivity, as well as response to Cu2+ within 20 min. Particularly, by introducing this probe into the paper-based device, we could achieve simple, high-throughput, visual and highly sensitive platform for POC detection of Cu2+. Finally, we assessed the paper-based device in real samples such as serum, cytochylema and lake water to demonstrate its promising application. As a result, satisfied performance for Cu2+ detection was achieved, which indicates the great potential of our strategy in the construction of POCT system for detecting analytes. Image 1 • Novel hybrid fluorophores based naphthofulorescein dyes have been synthesized to show excellent fluorescence properties. • Hybrid fluorophores-based paper device for visual detection of Cu2+ has been developed. • Suitable for point-of-care detection, the paper device could visualize high-throughput Cu2+ detection in real samples. [ABSTRACT FROM AUTHOR]

The article contains experiment to demonstrate fluorescent emission spectra of neon colored papers and plastic clipboards. The findings indicate that the shorter wavelength light is utilized by the “Daylight" pigment contained in these neon papers to enhance the reflected light in the longer wavelength regions thus making them appear brighter.