Apple Skin Research Articles

Antibacterial effect and mechanism of theaflavin against Listeria monocytogenes and its application on apple skins.

Theaflavin 3,3'-digallate (TF3), a major polyphenolic component of black tea, exhibits antibacterial effects against many foodborne pathogens. However, the antibacterial mechanisms of TF3 against Listeria monocytogenes remain unclear. In this study, we investigated the effects of TF3 on viability, biofilm, and membrane function of L. monocytogenes by the conventional plating method, crystal violet staining, and microscopy using fluorescent dyes JC-1 and Laurdan, respectively. It was found that TF3 showed excellent antibacterial activity against L. monocytogenes with the minimum inhibitory concentration of 62.5mg/L. The viable count determined on TSA decreased by 3log after the treatment for 2h with TF3 at 62.5mg/L. The viable count determined on TSA containing 4% NaCl decreased by more than 4log after the treatment for 30min with TF3 at the same concentration, suggesting that TF3 gave damage on the cells, enhancing the antibacterial action of 4% NaCl, but the damage was recoverable in the absence of 4% NaCl. To explore the antibacterial mechanisms of TF3, the effects of TF3 on membrane potential and membrane fluidity were investigated. TF3 reduced both membrane potential and fluidity of L. monocytogenes at 62.5mg/L, suggesting that TF3 damaged the structural integrity of the cell membrane. TF3 reduced biofilm mass of mature biofilm of L. monocytogenes. Moreover, THEAFLAVIN TF40, a commercially available Camellia sinensis leaf extract containing TF3, reduced viable count of L. monocytogenes by 2log on apple skin. These results suggest the potential of theaflavins as a natural anti-Listeria disinfectant.

The Development of Edible Straw from Apple and Durian Peel

Over the past few decades, there has been a surge in the demand for plastic utensils, especially plastic straw which contribute to consumption of toxic chemicals. The use of plastic straws has led to plastic pollution crisis due to their non-biodegradability and lengthy decomposition periods. Currently, various kinds of edible straw have been developed to replace traditional plastic straw to reduce the environmental pollution, however the edible straw usually has weak structural integrity and becomes soggy when immersed in beverages. The purpose of this study is to develop the production of edible straw from fruit peel, such as apple and durian peel skin and investigate the physicochemical characteristics of the edible straw at different temperatures. The manufacturing process of edible straw using fruit peel can be categorized into 3 main steps, including preparation of fruit peel paste using fruit peel and distilled water at weight ratio 1:0.3, preparation of edible film as well as drying and demoulding of edible straw. Then, a series of tests including water absorption test, heat resistance test and swelling ratio test have been conducted to investigate the functionality of the edible straw in different kinds of beverages, including hot and cold liquids at temperature ranges from 5 °C to 65 °C. The observation suggests that durian peel edible straw has higher water absorption capability, heat resistance and swelling ratio when soaked in liquids compared to apple peel edible straw. Both the apple and durian peel edible straw are best for use at beverage temperature within 25 °C. Durian peel edible straw has better performance as it can be used for beverage temperature up until 65 °C while only 45 °C for apple peel edible straw.

Silver-decorated three-dimensional ZnO nanoflowers enhancing the electromagnetic coupling for ultrasensitive SERS detection of multi-pesticide residues

—The development of sensitive analytical methods is of prime importance for the detection of pesticide residues on the surfaces of fruits and vegetables at extremely low concentrations. Here, we synthesized Ag-decorated three-dimensional ZnO nanoflowers (ZnO@Ag) composed of ultrathin nanosheets as surface-enhanced Raman spectroscopy (SERS) substrates. Combined with the finite-difference time-domain (FDTD) method, it is proven that the ultrathin nanosheets greatly improve the electromagnetic coupling between the two metal nanoparticles due to the high refractive index of ZnO and generate new “hot spots”. The nanosheets also endow the incident light with multiple reflections to motivate the local electromagnetic field. The substrate presents high sensitivity and the enhancement factor was as high as 2.98 × 107 utilizing R6G as probe molecules. The detection concentration of thiram and malachite green (MG) solutions can reach 10−10 M and 10−9 M, respectively. For the real-life sample assays, the substrate can simultaneously detect the two pesticides on apple skin with high sensitivity. The research also reveals the importance of semiconductors toward the local electromagnetic field enhancement in noble metal-semiconductor substrates, benefiting the realization of highly sensitive SERS substrates and the wide application of the SERS technology in real-world scenarios.

Optimisation of the extraction process of pectin polymer from red dragon skin (Hylocereus polyrhizus)

Background: The variation of pectin extracted from red dragon skin (Hylocereus polyrhizus) depends on the type of acid, temperature, and length of extraction time. Objective: This research was conducted to determine the characteristics of pectin produced from red dragon skin based on using citric, oxalic, and acetic acids at pH 4, extraction temperature of 60°C and 75°C, and duration of 120 minutes. Method: A total of six conditions for pectin extraction were performed and the obtained product was dried using the freeze-dryer. Furthermore, the optimisation included yield, moisture content (MC), equivalent weight (EW), methoxyl content (MeO), galacturonic acid content (GA), degree of esterification (DE), sugar and organic acid levels (SO), and Fourier Transform Infrared Spectroscopy (FT-IR) was performed. Result: The EW value of red dragon skin and commercial apple pectin were comparable but the MeO value was slightly different from those extracted with 75°C oxalic acid. Compared to commercial apple and orange skin, the GA value of red dragon pectin extracted with 75°C oxalic acid was not different. Conclusion: FT-IR spectra contained groups -OH, -CH, and C=O and were confirmed to have a GA structure. The best product was obtained by conducting extraction under the condition of 75°C for 120 minutes using oxalic acid.

A comparative study of distinguishing apple cultivars and a clone based on features of selected fruit parts and leaves using image processing and artificial intelligence

This study aimed to identify the most useful white-fleshed apple samples to distinguish apple cultivars and a clone. Whole apples, apple slices, seeds, and leaves belonging to ‘Free Redstar’, clone 118, ‘Ligolina’, ‘Pink Braeburn’, and ‘Pinokio’ were imaged using a digital camera. The texture parameters were extracted from images in color channels L, a, b, R, G, B, X, Y, Z, U, V, and S. The classification models were built using traditional machine learning algorithms. Models developed using selected image seed textures allowed the classification of apple cultivars and a clone with the highest average accuracy of up to 97.4%. The apple seeds ‘Free Redstar’ were distinguished with the highest accuracy, equal to 100%. Machine learning models built based on the textures of apple skin allowed for the clone and cultivar classification with slightly lower correctness, reaching 94%. Meanwhile, the average accuracies for models involving selected flesh and leave textures reached 86.4% and 88.8%, respectively. All the most efficient models for classifying individual apple fruit parts and leaves were developed using Multilayer Perceptron. However, models combining selected image textures of apple skin, slices (flesh), seeds, and leaves produced the highest average accuracy of up to 99.6% in the case of Bayes Net. Thus, it was found that including features of different parts of apple fruit and apple leaves in one model can allow for the correct distinguishing of apples in terms of cultivar and clone.

Combining the Use of Reflective Groundcovers and Aminoethoxyvinylglycine to Assess Effects on Skin Color, Preharvest Drop, and Quality of ‘Honeycrisp’ Apples in the Mid-Atlantic US

Apples are one of the most valuable fruits worldwide. ‘Honeycrisp’ is the top sales-producing cultivar in the US. Lack of red skin coloration and increased preharvest fruit drop significantly reduce the market value for cultivars such as ‘Honeycrisp’. The use of reflective groundcovers has been shown to enhance apple skin coloration. While the use of plant growth regulator AVG reduces fruit drop, it negatively affects skin coloration. Studies on the impacts of these practices in mid-Atlantic US-grown apples are limited. In this work, for two years, we compared differences in the light environment, fruit drop, internal ethylene concentration (IEC), physicochemical parameters, and skin coloration of ‘Honeycrisp’ apples in the lower third of the canopy. Apples were submitted to four treatment combinations of reflective groundcover (Extenday) and AVG (130 mg L−1). Assessments occurred throughout three ripening stages. Our results demonstrated that Extenday significantly promoted skin coloration (>75% blush) via the increased reflectance of photosynthetic photon flux density and UV radiation, and increased IEC, while also advancing fruit maturity, i.e., overripening. Conversely, AVG significantly minimized fruit drop and decreased EIC, delaying fruit maturity but drastically reducing red coloration (30–48% blush). The combined use of Extenday and AVG had a synergistic effect by decreasing fruit drop while enhancing fruit with >50% blush, without promoting overripening. Combining Extenday and AVG can boost the market value for ‘Honeycrisp’ apples in the mid-Atlantic US.

저온 저장 후지 사과의 과피와 과육 중 파이토케미컬 함량의 상관관계

This study determined the relationships between the total anthocyanin content in apple skin and the total polyphenols, flavonoids, proanthocyanidins, and soluble solids contents in the flesh of cold-stored Fuji apples. Total anthocyanin content in apple skin ranged from 0.130±0.005 mg CE/g fw to 0.262±0.028 mg CE/g fw, and the overall average was 0.200±0.008 mg CE/g fw. The total polyphenolic compounds in the flesh was ranged from a 4.283±0.141 mM GAE/g fw to 8.207±0.234 mM GAE/g fw, and the average content was 6.275±0.177 mM GAE/g fw. The total flavonoid content ranged from 4.510±0.080 mM QE/g fw to 2.467±0.458 mM QE/g fw, and the average total flavonoid content was about 3.586 mM QE/g fw. The total proanthocyanidin content was relatively high, ranging from 3.475±0.577 mM EE/g fw to 6.816±0.277 mM EE/g fw, and the soluble solid in the flesh was about 12 °Brix to 14 °Brix. The DPPH radical scavenging activity of extracts from apple flesh ranged from 66.36% to 94.99%, and the ascorbate equivalent concentration was 0.482 mM. The ABTS radical scavenging activity was 99.12% to 99.9%, indicating a higher inhibitory activity than the DPPH inhibitory activity, and the ascorbate equivalent concentration was 0.486 mM. The correlation between the total anthocyanin and total polyphenolic compounds was y = 15.192x + 3.2169 (R2=0.2748), but the concentration of total polyphenolic compounds increased when the total anthocyanin content was increased. The correlation equation of total anthocyanin with total flavonoids was y = 15.18x + 0.5555 (R2=0.6226), with total proanthocyanin was y = 14.918x + 2.3422 (R2=0.3372), and with soluble solid was y = 10.558x + 11.126 (R2=0.1925), indicating that the correlation of total anthocyanin with total flavonoid was higher than that with soluble solid.

Identification of Apple Fruit-Skin Constitutive Laws by Full-Field Methods Using Uniaxial Tensile Loading.

The protective and preservative role of apple skin in maintaining the integrity of the fruit is well-known, with its mechanical behaviour playing a pivotal role in determining fruit storage capacity. This study employs a combination of experimental and numerical methodologies, specifically utilising the digital image correlation (DIC) technique. A specially devised inverse strategy is applied to evaluate the mechanical behaviour of apple skin under uniaxial tensile loading. Three apple cultivars were tested in this work: Malus domestica Starking Delicious, Malus pumila Rennet, and Malus domestica Golden Delicious. Stress-strain curves were reconstructed, revealing distinct variations in the mechanical responses among these cultivars. Yeoh's hyperelastic model was fitted to the experimental data to identify the coefficients capable of reproducing the non-linear deformation. The results suggest that apple skin varies significantly in composition and structure among the tested cultivars, as evidenced by differences in elastic properties and non-linear behaviour. These differences can significantly affect how fruit is handled, stored, and transported. Thus, the insights resulting from this research enable the development of mathematical models based on the mechanical behaviour of apple tissue, constituting important data for improvements in the economics of the agri-food industry.

Detecting Multi-Scale Rose Apple Skin and Defects Using Instance Segmentation With Anchors Optimization

Detecting Multi-Scale Rose Apple Skin and Defects Using Instance Segmentation With Anchors Optimization

Determination of Polyphenolic Profile of Apple Pomace (Malus domestica Golden Delicious Variety) by HPLC-MS.

Apple (Malus domestica Borkh) is an appreciated source of polyphenols. Phenolic compounds are known as natural antioxidants and have a wide range of applications in different industries. Apple pomace has the potential of being an alternative source of polyphenols. To determine the polyphenolic profile of apple pomace, samples from the skin at two different stages of ripening were extracted with 80-20% EtOH-water/acetic acid 5% (S1) and 20-80% EtOH-water/acetic acid 5% (S2) in order to determine the solvent system. Ripe skins extracted with S1 showed a higher total polyphenol content or TPC (1.21 g of polyphenols per 100 g of fresh weight (FW)) than unripe apple skin, being the most effective system tested and a mean degree of polymerization of 2.47. Commercial apple pomace was extracted with S1, resulting in a TPC of 0.5615 ± 0.007 g of polyphenols per 100 g of FW. Meanwhile, the RP-HPLC-MS analysis led to the tentative identification of several polyphenolic compounds.

LAMP‐based detection of Monilinia fructigena, Monilinia polystroma and Monilinia fructicola in latently infected apple fruit

AbstractBrown rot in apples is caused by fungi belonging to the genus Monilinia and occurs annually in orchards with varying severity. The symptoms of the disease on apple fruits may occur during harvest and can also develop much later in storage. Therefore, from a practical point of view, it is very important to be able to test a sample of asymptomatic apples before putting them in storage or sending them to distant markets. Thus, there is a need to develop a quick and sensitive method of detecting disease causal agents in asymptomatically infected fruit. For this purpose, a procedure for DNA isolation from the skin of apples was developed, and a set of primers for the loop‐mediated isothermal amplification (LAMP) reaction was designed based on a fragment of the hsp60 gene encoding heat shock protein 60 of Monilinia fungi that are pathogenic to apple: M. fructigena, M. fructicola and M. polystroma. The method was validated by reactions with DNA from infected apple fruit exhibiting brown rot symptoms and DNA from infected apple fruit without visible brown rot symptoms (latent infection). To increase the sensitivity of detection before the LAMP reaction, preamplification of the target DNA was carried out. The sensitivity of detection in the LAMP assay for the DNA of all three tested species of fungi was 2 pg. The DNA preamplification significantly increased the sensitivity of Monilinia DNA detection to 0.1 pg. This study shows that the developed LAMP method can be used to detect Monilinia fungi in asymptomatically infected apples.

Comparative Analysis of Metabolites of 'Hongro' Apple Greasiness in Response to Temperature.

Greasiness in apple skin reduces its quality, and its level varies depending on the variety. In this study, low-temperature (1 ± 0.5 °C) stored 'Hongro' and 'Fuji', which had differences in the occurrence of greasiness, were moved to room temperature (20 °C) and untargeted metabolite and fatty acids for skin and flesh along with quality changes due to greasiness occurrence were compared. Ethylene production differed noticeably between the two varieties and increased rapidly in 'Hongro' until 9 d of room-temperature storage. The ethylene production did not differ significantly between the two varieties on day 20 when greasiness occurred. According to the PLS-DA score plot, while 'Hongro' had similar amounts of unsaturated and saturated fatty acids, 'Fuji' had approximately twice as much unsaturated-fatty-acid content. 'Hongro', after 50 d of low-temperature (1 ± 0.5 °C) storage, produced excessive ethylene during room-temperature storage, which was directly related to greasiness development. As a result, the primary wax components of greasy 'Hongro' were nonacosane and nonacosan-10-ol. As the room-temperature storage period elapsed, pentyl linoleate and α-farnesene contents increased significantly. Furthermore, these greasiness-triggering characteristics of 'Hongro' may have been genetically influenced by the paternal parent used during breeding.

The possibility of spreading herpes simplex virus type 1 via food handling and sharing.

Herpes simplex virus type 1 (HSV-1) is an enveloped virus that causes recurrent and incurable diseases in 67% of the world population. Although it is not listed as a foodborne virus, some studies have shown that it can be recovered from surfaces as well as food. We investigated its persistence at -20°C, 4°C, 20°C or 37°C for up to 7 days on stainless steel, aluminum, glass, polypropylene, cheddar cheese, sliced almond, and apple skin and in cola soft drink, orange juice, coffee, and milk as well as its transferability from stainless steel to dry or moistened nitrile or latex gloves over time at typical ambient temperatures. Based on plaque assay on Vero cells, HSV-1 persisted at least 24h on all surfaces and at least 1h on food matrices but was inactivated quickly in cola soft drink. Temperature and pH affected HSV-1 infectivity. Transfer of HSV-1 at a contact pressure of 1kg cm2-1 for 10s occurred only on latex, especially moistened. Our data on the persistence of HSV-1 on food-related surfaces suggest that some risk may be associated with sharing foods with infected carriers.

Prediction of membrane purification by membrane fouling based on mathematic and machine learning models combined with image processing technology

Apples have been widely cultivated due to their multiple functional nutrients such as polyphenols. In this study, polyphenol of apple skins were extracted and purified by ultrasound treatment and membrane filtration, respectively. The effects of feed liquid concentration, transmembrane pressure, and rotational speed on the purification of polyphenols by membrane filtration were mainly investigated. The efficiency of polyphenol purification was analyzed based on the particle deposition effect, steric rejection effect, and pectin sieving effect. Single and multi-stage Hermia models were applied to corroborate the aforementioned theory. The degree of membrane fouling was quantitatively analyzed using a self-written image processing program. The study compared the quantitative prediction models between the degree of membrane fouling and polyphenol purification using mathematical models and two machine learning (ML) models, namely Support Vector Machine Regression (SVR) and Back Propagation Artificial neural networks (BPNN). The degree of membrane fouling and the degree of polyphenol purification were used as input parameters and output parameters of the ML prediction model, respectively. The ratio of the training set (98 data points) and the test set (42 data points) was 7:3. The obtained results showed that the prediction efficiency of BPNN model (R2 =0.99968) outperformed the SVR model (R2 =0.97697), which was better than the mathematical model in terms of prediction performance due to the high generalization ability of the ML model and the high robustness of BPNN. The study provided an effective and accurate method for predicting membrane fouling and filtration purification. Thus, the use of ML as an artificial intelligence technique has a promising future in membrane separation and purification.

Ultraviolet B-induced increase of cyanidin-3-O-galactoside, quercetin-3-O-galactoside, and ursolic acid enhances antioxidant and anti-inflammatory activities in apples

Postharvest ultraviolet (UV) treatment is a promising method for enhancing the coloration of apple skin. However, the effects of this treatment on the bioactivities of apple skin components are not fully understood. This study aimed to evaluate changes in antioxidant and proinflammatory cytokine inhibition activities as well as the components of apple skin extracts following UV-B treatment. The results showed that UV-B treatment had minimal effects on the quality parameters of the fruit, such as firmness, soluble solids content, and titratable acidity, but it stimulated the accumulation of cyanidin-3-O-galactoside (C3gal). Quercetin-3-O-galactoside (Q3gal), quercetin-3-O-glucoside (Q3glu), and ursolic acid were the major components that exhibited significantly increased content in UV-B–irradiated apple skin extracts presenting 24.9, 7.9, and 11.1-fold higher content than dark treatment, respectively, with this study the first to reveal that UV-B treatment alters ursolic acid content in apples. UV-B treatment also increased both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid antioxidant activities, although excessive UV-B intensity (>4 W m−2 s−1) decreased DPPH activity. Furthermore, UV-B–treated skin showed significantly suppressed nitric oxide and tumor necrosis factor-α (TNF-α) production but not interleukin-6 (IL-6) inhibition, which was not a specific effect of UV-B treatment as it is common effect of apple skin extracts. C3gal and Q3gal significantly inhibited IL-6 but not nitric oxide and TNF-α suppression. Overall, our findings indicate that UV-B intensity positively correlates with antioxidant activity resulting from the accumulation of C3gal, Q3gal, Q3glu, and ursolic acid. However, UV-B intensity did not correlate with anti-inflammatory effects, although the extract of UV-B–treated apple skin exhibited relatively strong inhibition of inflammation.

Differential Coloration, Pigment Biosynthesis-Related Gene Expression, and Accumulation According to Developmental Stage in the ‘Enbu’ Apple

Coloration, a major factor contributing to apple quality, attracts consumer attraction, thereby increasing the sale of fruits in the market. Among the fruit pigments, anthocyanins and carotenoids are the most important pigments that impart coloration to apples. Pigment accumulation, which is regulated by transcriptional factors in the anthocyanin and carotenoid biosynthesis pathways, varies according to genetics, transcription, and developmental stage. To understand the regulation of color development in apples, we evaluated the expression of the genes in the anthocyanin and carotenoid biosynthetic pathways and analyzed the accumulation of pigment, including anthocyanin and carotenoid in the skin and flesh of the red-fleshed apple ‘Enbu’ cultivar at different fruit development stages (30, 60, 90, 120, and 150 days after full bloom, and ripe). Color development increased according to the developmental stage, with considerable variation in both the transcript levels and pigment concentrations observed in tissues, skin, and flesh. Moreover, we identified key transcription factors among the anthocyanin and carotenoid biosynthesis genes that regulated pigment accumulation. Pearson’s correlation analysis showed a strong correlation between the coloration patterns and the expression levels of anthocyanin biosynthesis-related genes (MdPAL, MdCHI, and MdF3H) and carotenoid biosynthesis-related genes (MdGGPPS, MdPSY, MdZDS, MdCRTISO, MdCRHβ, and MdZEP). This study provides insight into the molecular mechanisms underlying pigment biosynthesis for breeding high-quality red-fleshed apple varieties to cater to consumer attention and preference.

Exploring the potential of electrospun polymer-coated Ag nanofibers for synergistic SERS performance and real-world applications

Electrospinning is a prominent technique for fabricating polymer-stabilized composite nanofibers for surface-enhanced Raman scattering (SERS). However, further exploration of the surface chemistry of these electrospun composite substrates is crucial to manipulate the charge transfer (CT) effect and achieve synergistic effects between CT and localized surface plasmon resonance (LSPR) for enhanced bio-labeling and pesticide detection. Here, we present the development of a flexible and self-supporting SERS substrate using electrospinning, consisting of polymer-coated silver nanowires (AgNWs). By employing different polymer shells and probe molecules, we strategically adjusted the energy levels of the frontier orbitals, enabling effective control over the CT effect. The resulting nanofibers exhibited optimized selectivity and sensitivity through multiple CT routes, enabling the detection of thiram in apple skin using a convenient wiping sampling method with a low limit of detection (LOD) of 5 ng/cm². We also investigated other pesticides without viable CT routes to demonstrate the versatility of the composite substrates, although they exhibited relatively lower selectivity and sensitivity due to the absence of synergistic effects. This study highlights the potential of CT manipulation in harnessing synergistic effects in electrospun 2D composite nanofibers, thereby advancing the practical applications of SERS technology.

Pneumatic Defoliation Enhances Fruit Skin Color and Anthocyanin Pigments in ‘Picnic’ Apples

Apple skin color is essential for market value. Therefore, this study evaluated the efficiency of pneumatic defoliation (PD) on the enhancement of red skin color and anthocyanin pigments in ‘Picnic’ apples. Three weeks before harvesting, apple trees were treated with PD with low- (0.7 bar) and high- (0.9 bar) air pressure at a tractor driving speed of 2 km/h. Undefoliated trees served as controls. Higher leaf defoliation and leaf damage rates were observed in the high-PD treatment than those in the low-PD treatment. Photosynthetically active radiation inside the canopies was the highest in trees subjected to high-pressure PD than in those that underwent low-pressure PD and the controls. At harvest, the fruit color (a*) value, red-colored area, and anthocyanin content in the fruit skin were the highest in the high-PD treatment, intermediate in the low-PD treatment, and the lowest in the control treatments. Additionally, a higher expression of anthocyanin biosynthetic genes was observed in both defoliation treatments, especially under high PD. However, except for higher flesh firmness under low PD, the L* and b* values and fruit quality indices (fruit weight, starch pattern index, titratable acidity, soluble solids content, and sunburn occurrence) were not significantly affected by either PD treatment. In conclusion, PD can be used to enhance skin coloration and anthocyanin pigments in apples; further PD with high air pressure achieved optimum red skin coloration in ‘Picnic’ apples.

Ag microlabyrinth/nanoparticles coated large-area thin PDMS films as flexible and transparent SERS substrates for in situ detection

Flexible and transparent surface-enhanced Raman scattering (SERS) substrates haveattractedmuchattention as a fast, sensitive and in situ detection platform for practical applications. However, the large-area fabrication of flexible and transparent SERS substrates with high performance is still challenging. Here, a flexible and transparent SERS substrate based on large-area thin PDMS film decorated with Ag microlabyrinth/nanoparticles hierarchical structures (denoted as ALNHS@PDMS) is fabricated by using the floating-on-water method and magnetron sputtering technology. By optimizing the sputtering time, the ALNHS with multiple hot spots are uniformly distributed on the PDMS surface. Based on characterizing the rhodamine 6G (R6G) with a portable Raman spectrometer, the optimal ALNHS@PDMS film exhibits a high enhancement factor (5.2 × 106), excellent uniformity and reproducibility, as well as superior mechanical stability. In addition, thanks to the good sticky feature and bi-directional activation property of the thin ALNHS@PDMS film, the prepared flexible and transparent SERS substrate can achieve in situ detection of malachite green residues (10-6 M) on apple and tomato skins. This large-area, thin, mechanically robust, flexible and transparent ALNHS@PDMS film, integrated with a portable Raman spectrometer, shows great potential for point-of-care testing (POCT)in practical applications.

Modified paper-based substrates fabricated via electrostatic attraction of gold nanospheres for non-destructive detection of pesticides based on surface-enhanced Raman spectroscopy.

Flexible surface-enhanced Raman spectroscopy (SERS) substrates such as paper-based substrates show great potential for rapid detection of residual chemicals on food surfaces. However, controlling the density and distribution of metallic nanoparticles adsorbed on the paper is still challenging. The amount of gold (Au) nanospheres (51 ± 4 nm) attached on the filter paper modified with 3-aminopropyltriethoxysilane (APTES) was tunable, increasing as the level of APTES (2.5-15.0 g kg-1 ) applied for paper modification increased. Moreover, the Au nanospheres were relative evenly distributed on the filter paper modified with 2.5-10.0 g kg-1 of APTES, which resulted in excellent intra- and inter-reproducibility of SERS signals for pesticides including thiram, diquat dibromide, and paraquat dichloride (relative standard deviation = 2.2-10.1%). The modified paper-based substrate could be used to detect as low as 0.05-0.2 mg L-1 of pesticides in standard solutions, and as low as 5-20 ng cm-2 of residual pesticides on apple skins with minimum sample pretreatment. This paper-based substrate with tunable feature for the density and distribution of nanoparticles is applicable for rapid SERS detection of residual pesticides in fruits and vegetables. © 2023 Society of Chemical Industry.