Ratiometric fluorescent signals-driven smartphone-based portable sensors for onsite visual detection of food contaminants

Nanotechnology-adapted detection technologies could improve the safety and quality of foods, provide new methods to combat fraud and be useful tools in our arsenal against bioterrorism. Yet despite hundreds of published studies on nanosensors each year targeted to the food and agriculture space, there are few nanosensors on the market in this area and almost no nanotechnology-enabled methods employed by public health agencies for food analysis. This Review shows that the field is currently being held back by technical, regulatory, political, legal, economic, environmental health and safety, and ethical challenges. We explore these challenges in detail and provide suggestions about how they may be surmounted. Strategies that may have particular effectiveness include improving funding opportunities and publication venues for nanosensor validation, social science and patent landscape studies; prioritizing research and development of nanosensors that are specifically designed for rapid analysis in non-laboratory settings; and incorporating platform cost and adaptability into early design decisions. This Review presents a focused overview of nanosensor technology for ensuring the safety and quality of foods and discusses seven key challenges that are currently preventing their successful commercialization.

Challenges and potential solutions for nanosensors intended for use with foods.

Rapid, accurate, reliable, and risk-free tracking of pathogenic microorganisms at the single-cell level is critical to achieve efficient source control and prevent outbreaks of microbial infectious diseases. For the first time, we report a promising approach for integrating the concepts of a remarkably large Stokes shift and dual-recognition into a single matrix to develop a pathogenic microorganism stimuli-responsive ratiometric fluorescent nanoprobe with speed, cost efficiency, stability, ultrahigh specificity, and sensitivity. As a proof-of-concept, we selected the Gram-positive bacterium Staphylococcus aureus (S. aureus) as the target analyte model, which easily bound to its recognition aptamer and the broad-spectrum glycopeptide antibiotic vancomycin (Van). To improve the specificity and short sample-to-answer time, we employed classic noncovalent π-π stacking interactions as a driving force to trigger the binding of Van and aptamer dual-functionalized near-infrared (NIR) fluorescent Apt-Van-QDs to the surface of an unreported blue fluorescent π-rich electronic carbon nanoparticles (CNPs), achieving S. aureus stimuli-responsive ratiometric nanoprobe Apt-Van-QDs@CNPs. In the assembly of Apt-Van-QDs@CNPs, the blue CNPs (energy donor) and NIR Apt-Van-QDs (energy acceptor) became close to allow the fluorescence resonance energy transfer (FRET) process, leading to a remarkable blue fluorescence quenching for the CNPs at ∼465 nm and a clear NIR fluorescence enhancement for Apt-Van-QDs at ∼725 nm. In the presence of S. aureus, the FRET process from CNPs to Apt-Van-QDs was disrupted, causing the nanoprobe Apt-Van-QDs@CNPs to display a ratiometric fluorescent response to S. aureus, which exhibited a large Stokes shift of ∼260 nm and rapid sample-to-answer detection time (∼30.0 min). As expected, the nanoprobe Apt-Van-QDs@CNPs showed an ultrahigh specificity for ratiometric fluorescence detection of S. aureus with a good detection limit of 1.0 CFU/mL, allowing the assay at single-cell level. Moreover, we also carried out the precise analysis of S. aureus in actual samples with acceptable results. We believe that this work offers new insight into the rational design of efficient ratiometric nanoprobes for rapid on-site accurate screening of pathogenic microorganisms at the single-cell level in the early stages, especially during the worldwide spread of COVID-19 today.

Engineering of a Dual-Recognition Ratiometric Fluorescent Nanosensor with a Remarkably Large Stokes Shift for Accurate Tracking of Pathogenic Bacteria at the Single-Cell Level.

Reliable on-site monitoring of antibiotic residue is critical to establish the efficient pollution early-warning mechanism for ensuring food safety and environmental health. Herein, we reported the engineering of liposome-encapsulated aggregation-induced emission fluorogen into the portable smartphone for achieving the visual on-site detection of residual tetracycline (TC). Through nanoprecipitation, the aggregation-induced emission fluorogen (AIEgen) tetraphenylethene (TPE) was encapsulated into an amphiphilic phospholipid polymer, affording a scaffold to assemble Eu3+ for forming Eu3+-functionalized liposome-based AIEgen (Eu3+@AIEgen) with bright blue fluorescence at ~456 nm. Upon assistance of citrate, TC was capable of triggering the remarkable fluorescence color change from bright blue (~456 nm) to pink owing to the new red fluorescence emission appeared at ~611 nm, thereby emerging a significant dual-emission for ratiometric response. As expected, an ingenious citrate-assisted Eu3+@AIEgen liposome-based smartphone was proposed to precisely on-site report the residual levels of TC in real sample among the linear range of 0.0961–10.0 μM. Furthermore, this portable sensor exhibited a high sensitivity attributable to the low detection limit of 28.83 nM together with a fast response kinetics of 2.0 min for TC, agreeing well with the demands of on-site assay. This study showed the promising potential for utilizing AIEgen liposome to develop a new category of portable sensors for the point-of-care detection of antibiotic residue in complicated food and environment-related matrixes, which might open a novel way to establish efficient pollution early-warning mechanism for safeguarding public health.

Liposome-encapsulated aggregation-induced emission fluorogen assisted with portable smartphone for dynamically on-site imaging of residual tetracycline

As one of the most promising biomarkers for numerous malignant tumors, accurate and reliable reporting of Cathepsin B (CTSB) activity is of great significance to achieve efficient diagnosis of cancers at an early stage and predicting metastasis. Here, we report a vigorous ratiometric fluorescent method integrating a cancer-targeting recognition moiety with a remarkably large emission wavelength shift into a single matrix to report CTSB activity sensitively and specifically. As a proof of concept, we synthesized amine-rich carbon quantum dots (CQDs) with a blue fluorescence, which offered an efficient scaffolding to covalently assemble the nucleolin-targeting recognition nucleic acid aptamer AS1411 and a CTSB-cleavable peptide substrate Gly-Arg-Arg-Gly-Lys-Gly-Gly-Cys-COOH that tethered with a near-infrared (NIR) fluorophore chlorin e6 (Ce6-GRRGKGGC, Ce6-Pep), enabling a cancer-targeting and CTSB stimulus-responsive ratiometric nanoprobe AS1411-Ce6-CQDs. Owing to the efficient fluorescence resonance energy transfer (FRET) process from the CQDs to Ce6 inside the assembly of nanoprobe, the blue fluorescence of CQDs at ∼450 nm was remarkably quenched, along with an obvious NIR fluorescence enhancement of Ce6 at ∼650 nm. After selective entry into cancer cells via nucleolin-mediated endocytosis, the overexpressed CTSB in lysosome could cleave Ce6-Pep and trigger the Ce6 moiety dissociation from AS1411-Ce6-CQDs, thus leading to the termination of FRET process, achieving the efficient ratiometric fluorescence response toward endogenous CTSB with a remarkably large emission wavelength shift of ∼200 nm from NIR to blue emission region. Notably, the nanoprobe AS1411-Ce6-CQDs exhibited an excellent specificity for ratiometric fluorescent sensing of CTSB activity with an ultralow detection limit of 0.096 ng/mL, demonstrating its promising use for early precise cancer diagnosis in the near future.

Nucleolin-Targeted Ratiometric Fluorescent Carbon Dots with a Remarkably Large Emission Wavelength Shift for Precise Imaging of Cathepsin B in Living Cancer Cells.

Food pollution has aroused increasing public health concerns and poses a huge medical and ﬁnancial burden today. Here, we report a facile one-pot synthesis of hydrogen sulﬁde (H2S)-responsive near-infrared (NIR) ratiometric fluorescent nanoprobe NIR775/Cy7Cl@HyNPs by encapsulating H2S-sensitive organic chromic cyanine dye Cy7Cl and H2S-inert fluorophore NIR775 into an amphiphilic phospholipid polymer. Because of the conﬁnement effect of phospholipid layer, the loaded NIR775 and Cy7Cl could be brought in close proximity for fluorescence resonance energy transfer (FRET) to occur, leading to single emission of Cy7Cl at ∼ 810 nm inside nanoprobe NIR775/Cy7Cl@HyNPs. However, with the introduction of H2S, the FRET process from NIR775 to Cy7Cl is disrupted due to the stimuli-responsive chromic behavior as a result of H2S-triggered nucleophilic, leading to restoring of the fluorescence emission of NIR775 at ∼ 778 nm companied by a remarkable fluorescence decrease of Cy7Cl at ∼ 810 nm, thereby enabling nanoprobe NIR775/Cy7Cl@HyNPs to show a NIR ratiometric response toward H2S. As expected, the nanoprobe NIR775/Cy7Cl@HyNPs exhibits a prominent practicability to precisely report the levels of H2S in actual food mediums with a wide linear range of 0.0367–120.0 μM, a satisfactory limit detection of 11.0 nM, as well as an excellent specificity over other sulfur-containing substances (e.g. biothiols). This study emphasizes the promise for utilizing switchable chromic materials to develop a new category of NIR ratiometric ﬂuorescent nanosensors facilitating accurate and reliable measurement in actual food and agriculture-related systems without any pretreatments, which is of great signiﬁcance for safeguarding food safety and human health.

Rational engineering of chromic material as near-infrared ratiometric fluorescent nanosensor for H2S monitoring in real food samples

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Rational engineering of chromic material as near-infrared ratiometric fluorescent nanosensor for H2S monitoring in real food samples