Millions of microplastics released from a biodegradable polymer during biodegradation/enzymatic hydrolysis.

In this article, we show that enzymatic hydrolysis of a biodegradable polyester (poly(ε-caprolactone)) by Amano Lipase PS in an aqueous (buffer) environment yielded rapidly an excessive number of microplastic particles; merely 0.1 g of poly(ε-caprolactone) film was demonstrated to yield millions of particles. There were also indications of non-enzymatic hydrolysis at the same conditions, but this did not yield any particles within the time frame of the experiment (up to 6 days). Microplastic particles formed had irregular shapes with an average size of around 10 µm, with only a few reaching 60 µm. The formation of microplastic particles resulted from the uneven hydrolysis/erosion rate across the polymer film surface, which led to a rough and undulating surface with ridge, branch, and rod-shaped micro-protruding structures. The consequent detachment and fragmentation of these micro-sized protruding structures resulted in the release of microplastics to the surroundings. Together with microplastics, hydrolysis products such as acidic monomers and oligomers were also released during the enzymatic hydrolysis process, causing a pH decrease in the surrounding liquid. The results suggest that the risk of microplastic pollution from biodegradable plastics is notable despite their biodegradation. Special attention needs to be paid when using and disposing of biodegradable plastics, considering the enormous impact of the paradigm shift towards more biodegradable products on the environment.

Microplastics generated from a biodegradable plastic in freshwater and seawater.

Biodegradable polymers have been regarded as a promising solution to tackle the pollutions caused by the wide use of conventional polymers. However, during the biodegradation process, the material fragmentation leads to microplastics. In this work, the formation of microplastics from biodegradable poly (butylene adipate-co-terephthalate) (PBAT) in different aquatic environments was investigated and compared with the common non-biodegradable low-density polyethylene (LDPE). The results showed that a much larger quantity of plastic fragments/particles were formed in all aquatic environments from PBAT than from LDPE. In addition, UV-A pretreatment, simulating the exposure to sunlight, increased the rate of PBAT microplastic formation significantly. The size distribution and shapes of the formed microplastics were systematically studied, along with changes in the polymer physicochemical properties such as molecular weight, thermal stability, crystallinity, and mechanical properties, to reveal the formation process of microplastics. This study shows that the microplastic risk from biodegradable polymers is high and needs to be further evaluated with regards to longer timeframes, the biological fate of intermediate products, and final products in freshwater, estuarine and seawater natural habitats. Especially, considering that these microplastics may have good biodegradability in warmer 20 - 25° water but will most likely be highly persistent in the world's cold deep seas.

Selective surface-enhanced Raman scattering detection of Tabun, VX and Cyclosarin nerve agents using 4-pyridine amide oxime functionalized gold nanopillars.

We have earlier demonstrated sensitive detection of low the volatile nerve agents Tabun, Cyclosarin and VX by using handheld Raman instrumentation in conjunction with surface-enhanced Raman scattering (SERS) attained with gold and silver coated Si nanopillar substrates. In the present proof-of-concept study, the gold substrates chemically are functionalized to realize selectivity towards organophosphorus compounds (OPs) with high sensitivity. A potential capturer and reporter molecule, chemical nerve agent antidote, 4-pyridine amide oxime, is evaluated due to its high Raman cross section, high chemical affinity towards gold, and binding specificity to the target substances Tabun, VX and Cyclosarin via the oxime group. Upon selective and covalent binding, the SERS probe undergoes structural changes which are reflected in the spectral SERS responses, making it suitable for indirect monitoring of nerve agents in aqueous solution. With the probe attached to the hotspots of Au-coated Si nanopillars, the SERS signals distinctly discriminate between specific and non-specific analyte binding of Tabun, Cyclosarin and VX down to sub ppm levels. SERS spectrum of 4-PAO is measured after microliter drop coating of aqueous sample solution onto the functionalized substrates and subsequent water evaporation from surfaces. This binding assay is complemented by letting functionalized substrates being immersed into sample solutions 1 h before measuring. Binding specific SERS response decreases in following order: Tabun > VX > Cyclosarin. Overall, the concept looks promising, as expected the candidate probe 4-PAO introduces selectivity to the nanopillar gold substrates without loss of sensitivity.

Hue Parameter Fluorescence Identification of Edible Oils with a Smartphone.

Food fraud can be highly lucrative, and high accuracy authentication of various foodstuffs is becoming essential. Olive oil is one of the most investigated food matrices, due to its high price and low production globally, with recent food fraud examples showing little or no high quality olive oil in the tested oils. Here a simple method using a 405 nm LED flashlight and a smartphone is developed for edible oil authentication. Identification is fingerprinted by intrinsic fluorescent compounds in the oils, such as chlorophylls and polyphenols. This study uses the hue parameter of HSV-colorspace to authenticate 24 different edible oils of 9 different types and 15 different brands. For extra virgin olive oil, all nine samples are well separated from the other oil samples. The rest of the samples were also well type-distinguished by the hue parameter, which is complemented by hue-histogram analysis. This opens up opportunities for low-cost and high-throughput smartphone field-testing of edible oils on all levels of the production and supply chain.

Detecting forensic substances using commercially available SERS substrates and handheld Raman spectrometers.

Ultra-sensitive in-field measurements of most forensic substances still today remain a challenge for first responders and forensic investigators. Handheld Raman spectroscopy equipment is getting more and more routinely used in the field for evidence collection, however, restricted to measurements of pure or high concentration samples. Here, surface-enhanced Raman scattering (SERS) sensing of common forensic substances with commercially available SERS substrates and handheld spectrometers, have been investigated. 3D Finite Element Method (FEM) and Density Functional Theory (DFT) simulations were used to interpret the high SERS enhancement of the Ag nanopillar substrate and the detection of the substances, respectively. The forensic generality and high performance of the analytical method were demonstrated by explicit detection of close to unprecedented amounts, down to femtograms, of Cyclosarin, RDX, Amphetamine and Picric acid. Implications are ultra-sensitive in-field SERS detection of these substances with commercial equipment.

Hand-Held Femtogram Detection of Hazardous Picric Acid with Hydrophobic Ag Nanopillar SERS Substrates and Mechanism of Elasto-Capillarity.

Picric acid (PA) is a severe environmental and security risk due to its unstable, toxic, and explosive properties. It is also challenging to detect in trace amounts and in situ because of its highly acidic and anionic character. Here, we assess sensing of PA under nonlaboratory conditions using surface-enhanced Raman scattering (SERS) silver nanopillar substrates and hand-held Raman spectroscopy equipment. The advancing elasto-capillarity effects are explained by molecular dynamics simulations. We obtain a SERS PA detection limit on the order of 20 ppt, corresponding attomole amounts, which together with the simple analysis methodology demonstrates that the presented approach is highly competitive for ultrasensitive analysis in the field.

Detection of nerve gases using surface-enhanced Raman scattering substrates with high droplet adhesion.

Threats from chemical warfare agents, commonly known as nerve gases, constitute a serious security issue of increasing global concern because of surging terrorist activity worldwide. However, nerve gases are difficult to detect using current analytical tools and outside dedicated laboratories. Here we demonstrate that surface-enhanced Raman scattering (SERS) can be used for sensitive detection of femtomol quantities of two nerve gases, VX and Tabun, using a handheld Raman device and SERS substrates consisting of flexible gold-covered Si nanopillars. The substrate surface exhibits high droplet adhesion and nanopillar clustering due to elasto-capillary forces, resulting in enrichment of target molecules in plasmonic hot-spots with high Raman enhancement. The results may pave the way for strategic life-saving SERS detection of chemical warfare agents in the field.

Explosive and chemical threat detection by surface-enhanced Raman scattering: a review.

Acts of terror and warfare threats are challenging tasks for defense agencies around the world and of growing importance to security conscious policy makers and the general public. Explosives and chemical warfare agents are two of the major concerns in this context, as illustrated by the recent Boston Marathon bombing and nerve gas attacks on civilians in the Middle East. To prevent such tragic disasters, security personnel must be able to find, identify and deactivate the threats at multiple locations and levels. This involves major technical and practical challenges, such as detection of ultra-low quantities of hazardous compounds at remote locations for anti-terror purposes and monitoring of environmental sanitation of dumped or left behind toxic substances and explosives. Surface-enhanced Raman scattering (SERS) is one of todays most interesting and rapidly developing methods for label-free ultrasensitive vibrational "fingerprinting" of a variety of molecular compounds. Performance highlights include attomolar detection of TNT and DNT explosives, a sensitivity that few, if any, other technique can compete with. Moreover, instrumentation needed for SERS analysis are becoming progressively better, smaller and cheaper, and can today be acquired for a retail price close to 10,000 US$. This contribution aims to give a comprehensive overview of SERS as a technique for detection of explosives and chemical threats. We discuss the prospects of SERS becoming a major tool for convenient in-situ threat identification and we summarize existing SERS detection methods and substrates with particular focus on ultra-sensitive real-time detection. General concepts, detection capabilities and perspectives are discussed in order to guide potential users of the technique for homeland security and anti-warfare purposes.

Dimer-on-mirror SERS substrates with attogram sensitivity fabricated by colloidal lithography.

Nanoplasmonic substrates with optimized field-enhancement properties are a key component in the continued development of surface-enhanced Raman scattering (SERS) molecular analysis but are challenging to produce inexpensively in large scale. We used a facile and cost-effective bottom-up technique, colloidal hole-mask lithography, to produce macroscopic dimer-on-mirror gold nanostructures. The optimized structures exhibit excellent SERS performance, as exemplified by detection of 2.5 and 50 attograms of BPE, a common SERS probe, using Raman microscopy and a simple handheld device, respectively. The corresponding Raman enhancement factor is of the order 10(11), which compares favourably to previously reported record performance values.

Digital colour tone for fluorescence sensing: a direct comparison of intensity, ratiometric and hue based quantification.

The hue parameter of HSV colour-space for digital imaging is shown to be accessible for convenient quantitative fluorescence imaging. A commercially available pH probe was utilized in solution and incorporated into optical µ-sensors for microscopy applications.

Fluorescence ratiometric properties induced by nanoparticle plasmonics and nanoscale dye dynamics.

Nanoscale transport of merocyanine 540 within/near the plasmon field of gold nanoparticles was recognized as an effective inducer of single-excitation dual-emission ratiometric properties. With a high concentration of the signal transducer (ammonium), a 700% increase in fluorescence was observed at the new red-shifted emission maximum, compared to a nanoparticle free sensor membrane. A previously nonrecognized isosbestic point is demonstrated at 581.4 ± 0.1 nm. The mechanism can be utilized for enhanced and simplified ratiometric optical chemical sensors and potentially for thin film engineering to make solar cells more effective and stable by a broader and more regulated absorption.

A potential tool for high-resolution monitoring of ocean acidification.

Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acidification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and low oceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck for research on ocean acidification is long-term monitoring and the collection of consistent high-resolution pH measurements. This study presents a low-power (<1 W) small sample volume (25 µL) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatial resolution (approximately 15 s and 100 m between samples). A 405 nm light emitting diode and the blue and green channels from a digital camera was used for swift detection of fluorescence from the pH sensitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated by automated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegat region with a large range in salinity (~3-30) and temperature (~0-25°C). Ship-board precision of salinity and temperature adjusted pH measurements were estimated as low as 0.0001 pH units.

Diffusion consistent calibrations for improved chemical imaging using nanoparticle enhanced optical sensors.

A basic square root function was successfully used as a diffusion consistent calibration function that considers depletion mechanisms often occurring within optical chemical sensors. This continuous function improved image quality and simplified the calibration process. It may be a universal tool for the typical response function of reversible diffusion controlled sensing reactions. Further, we demonstrate that the gold nanoparticle interaction based ammonium fluorosensor is suitable for non-invasive high-resolution quantitative imaging of complex samples. The plasmon sensitized optical sensors were utilized as a bioanalytical tool for chemical imaging of natural degradation processes occurring in biological tissues. Analytical performance of the nanoparticle enhanced sensors confirmed superior sensitivity, reversibility, durability and overall image quality over non-doped sensing membranes. Although applied in a complex matrix of high potassium (major interferent) and very high sodium (interferent) excellent performance is achieved. The nanoparticle interaction/coextraction based sensing scheme utilized in this study is general and can be used for numerous ions, preferably combined with the diffusion consistent calibrations for superior analytical performance. A table with 44 commercially available ionophores is provided to guide potential users of this sensor configuration.

Plasmophore sensitized imaging of ammonia release from biological tissues using optodes.

A plasmophore sensitized optode was developed for imaging ammonia (NH(3)) concentrations in muscle tissues. The developed ammonia sensor and an equivalent non plasmophore version of the sensor were tested side by side to compare their limit of detection, dynamic range, reversibility and overall imaging quality. Bio-degradation patterns of ammonia release from lean porcine skeletal muscle were studied over a period of 11 days. We demonstrate that ammonia concentrations ranging from 10nM can be quantified reversibly with an optical resolution of 127 µm in a sample area of 25 mm × 35 mm. The plasmophore ammonia optode showed improved reversibility, less false pixels and a 2 nM ammonia detection limit compared to 200 nM for the non-plasmophore sensor. Main principles of the sensing mechanism include ammonia transfer over a gas permeable film, ammonia protonation, nonactin facilitated merocyanine-ammonium coextraction and plasmophore enhancement. The vast signal improvement is suggested to rely on solvatochroism, nanoparticle scattering and plasmonic interactions that are utilized constructively in a fluorescence ratio. In addition to fundamental medicinal and biological research applications in tissue physiology, reversible ammonia quantification will be possible for a majority of demanding imaging and non imaging applications such as monitoring of low ammonia background concentrations in air and non-invasive medicinal diagnosis through medical breath or saliva analysis. The nanoparticle doped sensor constitutes a highly competitive technique for ammonia sensing in complex matrixes and the general sensing scheme offers new possibilities for the development of artificial optical noses and tongues.

Plasmonic nanoparticle interactions for high-performance imaging fluorosensors.

We demonstrate a nanoparticle based ratiometric fluorosensor suitable for non-invasive high-resolution imaging of complex samples. Coextraction generates a movement of a solvatochromic dye, with a consequent shift from plasmophore coupled emission towards longer wavelength scattering enhanced emission. The nanoparticle doped sensors confirmed superior sensitivity, reversibility, durability and overall image quality.

Analytical performance during ratiometric long-term imaging of pH in bioturbated sediments.

In this study, the long-term analytical performance of a high-resolution ratiometric imaging sensor for pH was quantitatively determined. The sensor was applied in an experimental microcosm to illustrate biogeochemical consequences from mining activities by the chemosymbiotic bivalve Thyasira sarsi. Utilizing time-correlated pixel-by-pixel calibration protocols during imaging, close to 90% of the pixels were associated with a precision (S.D.) of <0.05 pH units at the end of an experimental period of 17 days. For comparison, a precision of <0.05 pH units was achieved for less than 50% of the pixels throughout experiments using conventional pre-sample calibration procedures. The average standard deviation of pixels was 0.01 pH units. Image analysis of single pixel derivatives and pH measurements over time suggested that T. sarsi affect pH distributions and general sediment geochemistry more than would be expected based on the small size of the bivalves. A significant decrease of pH in the overlying water suggested a considerable release of reduced compounds from the exhalent stream of the thyasirids. Strong pH gradients were demonstrated not only across the sediment-water interface but, also associated with bioturbation activities immediately adjacent to T. sarsi burrowing tracts, inhalant tubes and pedal tracts in the sediment matrix. Gradients of up to 1.16 pH units per mm were observed.

A high-performance fluorosensor for pH measurements between 6 and 9.

This study presents a high-performance ratiometric pH optode based on the fluorophore 6,8-dihydroxypyrene-1,3-disulfonic acid (DHPDS). The two pH-sensitive terminal hydroxy groups of DHPDS facilitated dual excitation/dual emission (F(1): lambda(1,ex)=420 nm, lambda(1,em)=462 nm; F(2): lambda(2,ex)=470 nm, lambda(2,em)=498 nm) properties for ratiometric (R(F1,F2)=F(1)/F(2)) normalization of sensor signal. The sensor demonstrated an exponentially decreasing ratiometric response with increasing pH, with a linear correlation (R(2)=0.9936) between (10)log(R(F1,F2)) and pH within the pH interval 6-9. Precision determined as the IUPAC pooled standard deviation for the pH values 6.00, 7.01 and 9.01, was 0.0057 pH units for the fluorosensor and 0.0054 for a commercially available pH electrode used for comparison. Between the end-points of calibration at pH 7.01, the precision of the sensor was 0.0037 pH units. Effects from changes in ionic strength (I(tot), 10-700 mM) were more pronounced for the electrode, with a linear (R(2)=0.9976) increase in response (deltaE/deltapH) with increasing I(tot). The DHPDS-based fluorosensor, however, retained sensitivity (delta(10)log(R(F1,F2))/deltapH=0.8024+/-0.0145), though with an overall increase in ratiometric signal with increasing I(tot). The preserved sensitivity despite changes in ionic strength was possibly a consequence from the dual photo-acidic properties of DHPDS. Analytical characteristics of immobilized DHPDS therefore not only facilitated high-performance measurements over a wide pH range, but also opened for straightforward simultaneous measurements of pH and ionic strength.

Plasmon enhancement and surface wave quenching for phase ratiometry in coextraction-based fluorosensors.

In this study, a novel fluorescence ratiometric sensing scheme is presented. Gold nanoparticles (GNPs) were lipophilized with dodecanethiol and incorporated in the ether phase of a coextraction based ammonium sensor. The novel concept of this sensing scheme is that the analyte response involves a movement of the fluorophore toward lipophilized GNPs in an organic phase. Properly arranged, the system benefits from surface plasmon enhancement as well as increased lossy surface wave quenching as the fluorophore moves toward the GNPs. Likely constructive scattering effects are also present due to some build-up of nanoparticle clusters. The sensor configuration significantly reduced the noise level, increased the ratiometric signal, and improved the limit of detection approximately 3 orders of magnitude as compared with the optical sensor without the nanoparticles and ion-selective ammonium electrodes. Qualitative and quantitative detection limits were 1.7 and 5.7 nM, respectively. The sensing scheme is versatile and can be utilized for many other ions.

An imaging pH optode for cell studies based on covalent attachment of 8-hydroxypyrene-1,3,6-trisulfonate to amino cellulose acetate films.

The objective of this study was to create a thin film optode for fast pH measurements that meets the requirements for imaging pH-responses from cells as well as for a future hybrid design for detection of multiple analytes simultaneously. The sensor is based on the covalent attachment of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) to a film forming cellulose acetate material through a sulfonamide linkage. The synthesis routes of the cellulose material and regio-specific covalent attachment of the dye are described in detail. The sensor was sterilized in two different ways and showed excellent biocompatibility with Chinese hamster ovary cells. Imprints from cells and mum thin cell extensions were visualized when altering pH of the surrounding solution. The sensor was tested together with time-dependent sigmoidal calibrations giving pH determinations with an exceptional precision and accuracy during measurement within pH 6-8. The precision of the optode, calculated as pooled S.D. (n=8) according to IUPAC recommendations between pH 6.641 and 7.742 was 0.0029. The accuracy was significantly better than the electrode used as reference during the measurements. The response time (0-95%) was 100s between pH 6.641 and 7.742 and the reverse response (95-0%) was 80s. The sensor shows great potential for extra-cellular pH determination over time during cell growth and pharmacological exposure.

A high-precision ratiometric fluorosensor for pH: implementing time-dependent non-linear calibration protocols for drift compensation.

We present a versatile time-dependent non-linear calibration protocol for optical sensors, implemented on the pH sensitive ratiometric fluorophore 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) immobilized in ethyl-cellulose. The calibration protocol individually compensated for the progressive drift of calibration parameters, whereby sensor precision and accuracy, as well as applicable lifetime were improved. A severely reduced photoacidity was observed for the immobilized fluorophore, for which excited state dynamics was characterized and benefited from during measurements. Due to the significantly reduced photoacidity of HPTS immobilized in the ethyl-cellulose sensing membrane, a dual excitation/dual emission (F(1), ex/em: 405/440 nm and F(2), ex/em: 465/510 nm) ratiometric (R(F(1), F(2) =F(1)/F(2)) sensing scheme could be used to amplify sensor response. The signal to noise (S/N) ratio was enhanced by approximately 400% utilizing the dual excitation/dual emission ratiometric sensing scheme, rather than the more commonly used protocol of dual excitation/single emission for HPTS fluorescence. Apparent pK(a) of the fluorophore ranged from 6.74 to 8.50, mainly determined by the immobilization procedure. The repeatability (IUPAC, pooled standard deviation) over three pH values (6.986, 7.702 and 7.828) was 0.0044 pH units for the optical sensor, compared to 0.0046 for the electrode used for standardization. Sensor analytical characteristics were thereby in principle limited by the performance of the standardization procedure.