Table 1.
Colorimetric sensing systems for the detection of pathogenic bacteria and toxins a.
| Material | Receptor | Target | Linear Range | LoD | Assay Time | Real Sample to Be Tested | Driving Force of Color Change | Feature | References |
|---|---|---|---|---|---|---|---|---|---|
| AuNPs, magnetic beads | Monoclonal antibody, polyclonal antibody | Listeria monocytogenes | 1.1 × 102 CFU/mL–1.1 × 106 CFU/mL | 100 CFU/mL | 30 min | Lettuce samples | Induction of pH change | Use of magnetic nanobeads modified with urease and monoclonal antibodies. | [19] |
| Use of AuNPs modified with urease and polyclonal antibodies. | |||||||||
| Use of BCP. | |||||||||
| AgNPs | Monoclonal antibody | Salmonella typhimurium | 1 × 108 CFU/mL–1 × 101 CFU/mL | 100 CFU/mL | Apple juice, lake water sample | Induction of pH change | Based on the competitive binding ability of urease and bacterial cells to PEI-functionalized AgNPs. | [20] | |
| Ag ion | None | S. typhimurium | 1 × 107 CFU/mL–1 × 101 CFU/mL | 100 CFU/mL | Tap water | Induction of pH change | Based on the Ag-induced inhibition of urease activity and Ag ion utilization. | [21] | |
| Combined with electrochemical sensing. | |||||||||
| NPs | Aptamer | Escherichia coli., S. typhimurium | 1 × 105 CFU/mL–1 × 101 CFU/mL | 1 CFU/mL | <1 h | Milk | Induction of pH change | Use of pH-responsive NPs made of phenolphthalein (PP) and thymolphthalein (TP) indicators. | [22] |
| Combined with automated equipment. | |||||||||
| Allows multiplexing detection. | |||||||||
| Filter paper | None | Bacteria | 11.2 × 103–1.12 × 106 CFU/g (using BTB), 38.0 × 103–1.12 × 106 CFU/g (using BCP) | 11.64 × 103 CFU/g | Chicken and meat samples | Induction of pH change | Monitoring of bacterial contamination level using paper-based pH indicators, BTB, and BCP. | [23] | |
| Sensing of external pH change caused by volatile basic nitrogen generated from bacterial spoilage. | |||||||||
| Use of RGB analysis software on a smartphone. | |||||||||
| Filter paper | None | E. coli, E. coli O157:H7, L. monocytogenes, Vibrio vulnificus | 1 × 106–1 × 108 CFU/mL | 10 CFU/mL | 1 h | Milk | Chemical reaction between intracellular enzymes and their chromogenic substrates | One-step-based 3D paper sensor functionalized with lysing and oxidizing agents. | [31] |
| Filter paper | None | E. coli, E. coli O157:H7 | 1 × 106–1 × 109 CFU/mL | 10 CFU/mL | <4 h | Milk | Chemical reaction between intracellular enzymes and their chromogenic substrates | Use of a multi-layered paper structure. | [32] |
| Use of β-glucuronidase and β-galactosidase-based enzymatic reactions. | |||||||||
| None | None | Staphylococcus aureus, E. coli | 2.6 × 102–1.16 × 109 CFU/mL (for E. coli), 9.75 × 102–6 × 109 CFU/mL (for S. aureus) | ND | 2 h | Drinking water, milk | Redox reaction between the cell counting kit-8 (CCK-8) solution and dehydrogenase | Measurement of formazan generated from the reduction reaction between dehydrogenase and CCK-8 (containing WST-8 and 1-methoxy-5-methylphenazinium methyl sulfate). | [33] |
| None | None | E. coli | 1 × 104–1 × 109 CFU/mL | 1 × 104 CFU/mL | 1 h | Unfiltered tap water | Reduction reaction of p-benzoquinone by intracellular enzymes | Use of RGB analysis software on a smartphone for quantification. | [34] |
| Filter paper | None | E. coli, S. aureus, Enterococcus faecalis, Streptococcus mutans, Salmonella pullorum | 1 × 104–1 × 108 CFU/mL | 7.48 × 103 CFU/mL (for E. coli) and 3.3 × 103 CFU/mL (for S. aureus) | 20 min | Inhibition of GOx activity by glucose uptake of bacterial cells | Use of starch–iodide doping paper as a substrate. | [35] | |
| Based on the conversion from iodide to iodine by H2O2 involving GOx-mediated glucose oxidation (causing color change of starch–iodine) and glucose uptake of bacterial cells (causing inhibition of color change of starch–iodine). | |||||||||
| Filter paper | None | E. coli | 1 × 102–1 × 106 CFU/mL | 44 CFU/mL | Tap water, degrease milk | Inhibition of color change of OPD via Cu2+ reduction by intracellular enzymes | Use of paper as a substrate. | [36] | |
| Based on the competitive reaction between the oxidation of OPD by Cu2+ (causing color change of OPD) and the reduction of Cu2+ by bacteria (causing inhibition of color change of OPD). | |||||||||
| Use of RGB analysis software on a smartphone for quantification. | |||||||||
| Allows dual-readout assay (colorimetry and fluorescence). | |||||||||
| ZnFe2O4/rGO | Aptamer | S. typhimurium | 11–1.10 × 105 CFU/mL | 11 CFU/mL | None | Peroxidase-like catalytic reaction of the ZnFe2O4/rGO nanostructure | Shows highly stable catalytic activity at low pH (over 5.5) and high temperature (over 50 °C). | [37] | |
| Cu2-rGO NPs | None | Salmonella spp. | 1.93 × 101–1.93 × 105 CFU/mL | 0.51 CFU/mL | Milk | Peroxidase-like catalytic reaction of GO | Use of dsDNA amplified via PCR from cells. Based on the competitive binding of bacterial dsDNA and Cu2-rGO NPs to TMB. | [38] | |
| Graphitic-C3N4@Cu2O | Aptamer | S. typhimurium | 1.5 × 101–1.5 × 105 CFU/mL | 15 CFU/mL | 6 min | Milk | Peroxidase-like catalytic reaction of the g-C3N4@Cu2O nanostructure | Based on the competitive binding of the aptamer and g-C3N4@Cu2O to TMB. | [39] |
| Fe3O4/Au magnetic nanocomposite | Antibody, aptamer | S. aureus | 1 × 101–1 × 106 CFU/mL | 10 CFU/mL | Pork, milk | Peroxidase-like catalytic reaction of AuNPs by H2O2 etching | Use of a magnetic nanocomposite consisting of a Fe3O4 core and an Au shell as a capture probe. | [40] | |
| Use of Apt–AuNPs as a signal amplifier. | |||||||||
| AuNPs, magnetic beads | Antibody | Brevotoxin B | 0.1–150 ng/kg | 0.076 ng/kg | Seafood sample | Peroxidase-based TMB oxidation reaction | Addition of Fe2+ for color signal amplification. | [41] | |
| Magnetic beads | Antibody | Ochratoxin A | 0.01–10 ng/mL | 8.3 pg/mL | 30 min (for color development) | Red wine sample | Enzyme-controlled Turnbull’s blue generation | Based on the formation or inhibition of Prussian blue from K3[Fe(CN)6] via GOx-catalyzed H2O2 production. | [42] |
| Aptamer@ BSA- AuNCs |
Aptamer | S. typhimurium | 1 × 101–1 × 106 CFU/mL | 1 CFU/mL | Eggshell, Egg white | Peroxidase-like catalytic reaction of AuNCs | Based on the enhanced catalytic activity of a cell-bound nanostructure (cell-aptamer@BSA-AuNC composite). | [43] | |
| MnO2-doped Fe3O4 NPs | None | S. aureus, Vibrio parahaemolyticus | 1 × 101–1 × 106 CFU/mL | 1 × 102 CFU/mL | Lake water sample | Peroxidase-like catalytic reaction | Use of multifunctional NPs for recognition, absorption, and separation of the analyte. | [44] | |
| Exhibits the catalytic activity of TMB in the presence of oxygen in a solution without H2O2. | |||||||||
| AuNPs | 4-MPBA | E. coli | 1 × 104–1 × 107 CFU/mL | 1.02 × 103 CFU/mL | 20 min | Drinking water | Salt-induced aggregation | Use of AuNPs functionalised with 4-MPBA, which binds to LPS and peptidoglycan existing on the surface of gram-negative and gram-positive bacterial cells, respectively. | [48] |
| Use of RGB analysis software on a smartphone for quantification. | |||||||||
| AuNPs | Aptamer | Shigella flexneri | 1 × 102–1 × 106 CFU/mL | 80 CFU/mL | 20 min | Salmon | Salt-induced aggregation | Use of aptamers that can bind to bacterial cells rather than AuNPs. | [49] |
| AuNPs, silica nanoparticles (SNPs) | Aptamer | Aflatoxin M1 | 300–75,000 ng/L | 30 ng/L | Milk | Salt-induced AuNP aggregation | Salt-induced aggregation by releasing complementary strands from aptamer-modified SNPs in the presence of the target. | [50] | |
| AuNPs, magnetic nanoparticles (MNPs) | Antibody | V. parahaemolyticus | 1 × 101–1 × 106 CFU/mL | 10 CFU/mL | Oyster | Mn2+-induced AuNP aggregation | Combination with the signal amplification method based on ascorbic acid-mediated Mn2+ reduction and a sandwich assay using IgG-MnO2 NPs and IgY-MNPs. | [51] | |
| AuNPs | Chimeric phage | E. coli, V. cholerae, Pseudomonas aeruginosa, Xanthomonas campestris | 1 × 102 CFU/mL | <1 h | Sea water, tap water | AuNP aggregation | Use of thiolated chimeric phages that can bind to both bacterial cells and AuNPs | [52] | |
| AuNPs | Chimeric phage | P. aeruginosa | 1 × 101–1 × 106 CFU/mL | 1 × 102 CFU/mL | ~30 min | Drinking water, non-fat bovine milk | AuNP aggregation | Detection of antibiotic resistance/susceptibility of bacterial cells | [53] |
| Dextran-coated AuNPs, MNPs | Antibody | E. coli | 1 × 103–1 × 106 CFU/mL | 41 CFU/mL | 95 min | Milk | ConA-driven aggregation of dextran-coated AuNPs | Use of ConA with pH-regulated transformation ability of dimers/tetramers | [54] |
| AuNPs | Fumonisin B1 (FB1) | 2–8 mg/kg | 0.9 mg/kg | Corn | Hydrolyzed FB1-induced AgNP aggregation | Use of cysteamine-functionalised AuNPs (Cys-AuNPs). Need for NaOH treatment to obtain hydrolyzed FB1 with a high affinity towards Cys-AuNPs. | [55] | ||
| AuNPs | DNA | S. aureus | 1–1 × 105 CFU/mL | 1 CFU/mL | 15 min | CSF, urine, spit, serum | Enzyme-driven DNA walker-induced AgNP aggregation | Use of an exonuclease III-driven DNA walker system for signal amplification. | [56] |
| AuNPs, MNPs | Aptamer | S. typhimurium | 1 × 102–1 × 106 CFU/mL | 2.4 × 102 CFU/mL | Milk | Catalytic hairpin assembly (CHA)-driven AuNP aggregation | Use of Y-shaped CHA for signal amplification. | [57] | |
| AgNPs | Antibody | Staphylococcal enterotoxin B | 0–2 ppm | 0.5 ppm | 15 min | Milk, honey | AgNP accumulation | Use of AgNP-based sandwich-type lateral flow immunoassay (LFIA). | [65] |
| AuNPs | Antibody | S. enteritidis | 1 × 105–1 × 108 CFU/mL | 1 × 104 CFU/mL | 20 min | Milk | AuNP accumulation | Use of LFIA. | [66] |
| Use of a signal enhancer, HAuCl4 and NH2OH·HCl for in situ AuNP growth. | |||||||||
| AuNPs | Antibody | V. parahaemolyticus | 4.66 × 105 CFU/mL | 2 h | Oyster hemolymph | AuNP accumulation | Use of a dipstick. | [67] | |
| AuNPs | Aptamer | S. typhimurium, E. coli O157:H7, S. aureus | 1 × 103 CFU/mL for S. typhimurium and 1 × 104 CFU/mL for E. coli O157:H7 and S. aureus | 10 min | Milk, chicken, food | AuNP accumulation | Use of LFA. | [68] | |
| AuNPs, MNPs | Aptamer | V. parahaemolyticus | 1 × 103–1 × 108 CFU/mL | 2.6 × 103 CFU/mL | 67 min | Shrimp | AuNP accumulation | Combination of HCR-mediated signal amplification methods. | [69] |
| AuNPs | Antibody | E. coli O157:H7 | 1.25 × 101–1.25 × 105 CFU/mL | 1.25 × 101 CFU/mL | Milk | AuNP accumulation | Use of LFA. | [70]; | |
| Combination of two signal amplification strategies; use of a signal enhancer (hydroquinone) for in situ AuNP growth and nanozyme-mediated catalytic deposition. | |||||||||
| Pd-Pt NPs | Antibody | E. coli O157:H7 | 1 × 102–1 × 106 CFU/mL | 0.87 × 102 CFU/mL | 10 min | Milk | Pd-Pt NP accumulation-driven catalytic reaction | Use of LFA. | [71] |
| Signal readout by oxidised TMB through Pd-Pt NP-mediated catalytic reactions. | |||||||||
| Pt-Au NPs | Antibody | E. coli O157:H7 | 1 × 102–1 × 108 CFU/mL | 1 × 102 CFU/mL | 1 min | Pt-Au NP accumulation-driven catalytic reaction | Use of LFA. | [72] | |
| Use of Pt-Au-mediated signal amplification. |
a Abbreviations: LoD, limit of detection; AuNPs, gold nanoparticles; CFU, colony-forming unit; TMB, 3,3′,5,5′-tetramethylbenzidine; BTB, bromothymol blue; BCG, bromocresol green; BCP, bromocresol purple; RGB, red-green-blue; PCR, polymerase chain reaction; PEI, polyethylenimine; WST-8, 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt; OPD, o-phenylenediamine; dsDNA, double-stranded DNA; GO, graphene oxide; rGO, reduced GO; BSA, bovine serum albumin; GOx, glucose oxidase; AuNCs, gold nanoclusters; 4-MPBA, 4-mercaptophenylboronic acid; LPS, lipopolysaccharide; CSF, cerebral spinal fluid; ConA, concanavalin A; HCR, hybridization chain reaction; ND, not determined.