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Methods of selective fluorescent sensing of small organic molecules require the use of biomolecules or complicated synthesis of artificial probes. An alternative technique is aggregationbased sensing based on the response generated due to self-assembly effects rather than by direct analyte−probe interaction. We have found that far red/near IR emission of spinach chlorophyll a at 680 nm is selectively enhanced by multiply charged aminoglycoside cations in the presence of anionic surfactants, whereas such an effect is not observed for smaller species. Selectivity of the detection is controlled by a positive charge of the drug and its ability to form multiple noncovalent bonds, as well as by the nature of the surfactant (n-dodecyl sulfate or lauroyl sarcosinate is preferable). Fluorescence of chlorophyll is enhanced due to its solubilization in the drug− surfactant aggregate. We have developed a simple and selective method for the detection of aminoglycoside antibiotic neomycin in urine samples with a limit of detection of 6 μM. The development path for aggregation-based analysis of other systems using chlorophyll is outlined.

1IntroductionNon-invasived iagnostics( excludingn ot only blood probing, but even skin damage) becomes more and more importantn owadays [1][2][3][4].E xhaled breath condensate (EBC) is the non-invasively collected excretory liquid of high diagnostic potential [5][6][7][8].H owever, metabolite concentration in excretoryl iquids is usually much less than in blood, dictating as earch fore xpressa nalyticalt ools with improved sensitivity.Lactate is amongt he most important compounds for clinicald iagnostics being am arker for glycolysis,a naerobic metabolism,w hich causes death of tissues.S port medicine requires monitoring of lactate for training as well for evaluatingo ft he so-called "lactate threshold" [9][10][11] indicating physical trainingl evel of as portsman. Being ap roducto ff ermentation [12],l actate can be useda s am arker for naturalness of food products. It is not surprising that the lactate sensitive electrode was amongt he first biosensors elaborated [ 13].S ince that time an umber of lactate biosensors were reported [14][15][16][17][18][19][20] including the most recent and advantageous ones based on Prussian Blue modified electrodes [21][22][23].H owever,t he lower detection limits of the reported systemsa re alwaysa bove 1 mM, whereas metabolite content in excreted liquidsc an be lower, knowing that theird ilution factorv ersusb lood can reach the value of 1000, and the blood lactate content is in the range from 0.5 to 2.0 mM.Pre-concentrationi sapowerful tool providing after combination with ac ertain detectionp rinciple the significantly decreased lower detection limit. In addition, preconcentrationi sasimple technique allowing sample separation from different interferingc ompounds thus improving selectivity of analysis [24].with pre-concentration which are advantageous over con-ventionalF IA combined with as imilar biosensor are:( i) the 50 times improved sensitivity (7.0 Acm À2 M À1 )a nd (ii) the calibration range shifted by almost two orders of magnitude towards lower analyte concentrations.T he developed FIA system was tested for lactate detection in exhaled breath condensate samples collected from pulmonary patients and sportsmen.

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